By the time Johnny Galecki took a step back from Hollywood, he had built a remarkable legacy in comedy. With extensive experience from his roles in “The Big Bang Theory,” “Roseanne” as David, and a diverse range of films like “A Night in the Life of Jimmy Reardon,” “CBGB,” and “National Lampoon’s Christmas Vacation,” Galecki’s comedic talent was evident both on-screen and off-screen. Known for bringing humor to the set, he often amused his colleagues, whether through a missed line, a light-hearted prank, or inadvertently walking into a scene at the wrong time. A signature move of his was shouting “Balls!” whenever a mistake sent the crew into fits of laughter, demonstrating his unique comedic style and ability to entertain his co-stars.

We’ve compiled a collection of “The Big Bang Theory” bloopers showcasing Galecki’s knack for keeping his colleagues entertained. Laughter is said to be the best medicine, and this compilation of gaffes, forgotten lines, and overly enthusiastic laughs proves this point quite effectively. Here are 17 instances where Johnny Galecki managed to make his fellow cast members break character.

In one blooper from Season 1, Johnny Galecki portrays Leonard Hofstadter’s annoyance over Penny’s (played by Kaley Cuoco) choice to date someone else, leading to a humorous slip-up. When questioning if there’s another person in her apartment, he mistakenly addresses Penny instead of Cuoco’s character, prompting his co-star to correct him with a gentle reminder, “I’m Penny.” This hilariously triggers Galecki to erupt in laughter and exclaim in frustration as he humorously retreats to prepare for another take.

It’s a blooper that manages to show off how easily and quickly the “Big Bang Theory” team’s chemistry came together. In particular, it presages how well Galecki and Cuoco were getting on during this time period. Fairly soon, the pair would get together in real life. They wound up dating for quite a while, in spite of their age difference, forging a connection that lasted for two years before they broke up and began seeing other people.

In this Season 3 “Big Bang Theory” blooper, a bearded and depressed Leonard tries to apologize to Penny for his behavior upon returning from a summer of isolation at the North Pole with the rest of his friends in order to complete an important scientific experiment. He explains away the behavior that caused him to disappear, and they make amends — a peace that will not last once Sheldon (Jim Parsons) figures out that the can opener they were using in their shelter had interfered with their data.

Unfortunately for Galecki, filming his big speech didn’t go smoothly. The big blocks of dialogue he was required to speak are so long that he quickly runs out of breath while trying to get through it all. Though he tries valiantly to stay on script, he runs out of steam and needs to pause to breathe. That makes Kaley Cuoco burst into giggles right on screen — and leaves Galecki looking for a better way to pace himself. It’s a blooper as quick as Galecki’s speech — and just as much fun.

Not every nerd is a hooper, but during an early fight between “The Big Bang Theory’s” primary twosome, Leonard tries to prove to Penny that he’s got some level of athletic skill when he tries to toss a binder into a trash bin in Season 2. Unfortunately for Leonard — and Johnny Galecki — his first attempt at tossing the binder away results in it bouncing off of the top of the trash can. Kaley Cuoco sarcastically compliments the actor’s prowess while trying to keep it together, but Galecki cracks, which then causes his co-star to burst out laughing.

In the version of the scene that aired, Galecki manages to make the basket, and Leonard comes off as an athletic hero — well, as much as he ever is during the course of the series. Some nerds have all the luck — and some bloopers have all the charm.

Sometimes, it’s the simplest of lines that catch an actor off-guard. In this Season 3 blooper, Johnny Galecki trips over what he describes as “the easiest word in the line” — “prepared.” Galecki actually manages to mess up the word twice, stopping his speech in the exact same place both times, and finally cursing when it refuses to come out of his mouth.

The mistake makes Jim Parsons promptly break into laughter both times, which sets the rest of his castmates off into gales of chuckles that no one can really control. During the second blown take, Kunal Nayyar even jumps up and down while clapping his hands, unable to contain his glee at Galecki’s foibles. It’s one of those moments where no one’s really in control of their laugh reflex, but everyone’s able to get a chortle in before they roll for the next take.

Leonard and Penny are deeply committed to one another by the time Season 3 rolls around, which means there are plenty of moments where they cuddle up and try to carve out a little alone time— in spite of the fact that Sheldon interferes in their love story as often as he can. This time, when they get together for a quiet night on the couch, Kaley Cuoco manages to deliver Penny’s remarks perfectly, happily declaring that it’s nice to have the entire apartment to themselves again after another day of dealing with their friends. But Johnny Galecki can’t get out the right words, even though the line seems to be deceptively simple.

“Ra … it … oh,” Galecki remarks, which causes Kaley Cuoco to break into laughter before hugging him. Sometimes the simplest of mistakes cause the biggest laughs to burst forth from an actor’s soul.

It’s rare when someone else’s mistake causes another actor on the set to make a remark that makes the whole cast crack up, but that’s exactly what happens when Kaley Cuoco messes up a line while trying to give voice to Penny’s frustration over how the rest of the gang perceives her. “My point is, I do not judge a book by its cover,” is what she intended to say, but she trips up at the word cover, saying “spine” instead. She just can’t get the word out. Johnny Galecki then points toward her and simply says, “Hi.” That cracks Cuoco up, along with everyone else in the scene. Managing to amuse everyone in the room with a simple point of the finger and one word, it’s clear that Galecki definitely knows how to make them laugh and keep them coming back for more.

This one doesn’t involve Johnny Galecki — at least at first. Kaley Cuoco and Jim Parsons are fighting it out as Penny and Sheldon in the kitchen of Sheldon and Leonard’s apartment. Penny has spent the night with Leonard, only to find herself having to face down a grumpy Sheldon the following morning. Penny offers Sheldon some French toast, which he rejects by informing her that it’s oatmeal day. This is when Cuoco breaks character as she notices Galecki has entered the room, jumping his cue by several beats. “Hi, Johnny,” she says, which cracks up Parsons and Galecki.

“I woke up a little early this morning,” Galecki quips as the scene resets. While the early bird might get the worm, it looks like the joke ended up being on everyone in this clip.

This one takes an actual line of dialogue from the script and turns inward on itself, resulting in a meta joke that the live audience gets and the actors can’t resist laughing at, turning the jest into a rapid-fire quipfest.

The scene begins with Penny, in a moment of disgust, asking Raj if he’s high. Johnny Galecki has the next line, but whatever he intends to say is incoherently garbled as the words fail to come to him in the correct order. Cuoco cracks up, as does an off-camera Jim Parsons. Cuoco returns to her scripted lines, moving toward Galecki and wondering out loud if he’s high. Galecki holds up his left hand, his fingers held a few centimeters from one another — the international symbol for “a little bit.” Sober or just a little bit stoned, the interaction still manages to make the whole gang giggle.

What’s supposed to be a supportive and perhaps surprisingly emotional scene between Raj and Leonard as they discuss the best practices for wooing the opposite sex devolves due to a vaguely ribald joke in this clip. Raj is confused when Leonard says he would “put on a show” for Penny when they get frisky. “What do you mean, you’d put on a show?” Raj asks Leonard. “You know, like the way I took my clothes off,” Leonard responds, accenting his words with a slight shoulder shake.

It’s likely the impulsive shoulder shimmy that Johnny Galecki added to the line that sets Kunal Nayyar to giggling, because while he tries to hold it all together with an incredulous reaction, he instead breaks immediately. Galecki responds by moving his shoulders even more and putting on a flirtatious expression, trying to wring even more laughter out of his co-star. By the end of the clip, he’s leaning over the chair, and Nayyar is still laughing. Is it any wonder that Nayyar admitted he’s still not over “The Big Bang Theory” being off the air?

Another Kunal Nayyar and Johnny Galecki clip sees Nayyar crack his co-star up by blowing his lines — and then Galecki one-ups him by climbing into bed with him and making him laugh even harder.

The blooper begins with Leonard bemoaning the fact that Raj is using his bed to sleep in instead of sticking to his own room. Raj begins to explain that his room is occupied, so he’s borrowing Leonard’s for the moment. “Well, I would’ve slept in my own bed, but it was being used to disgrace …” It’s here that Nayyar drifts off and fails to stick the landing, cracking himself up. Galecki responds by crawling into bed with Nayyar and making him laugh even harder. The two embrace while laughing at the situation, slapping each other on the back while they roll around under the sheets. Talk about lying down on the job!

Johnny Galecki and Kaley Cuoco often found themselves giving voice to Penny and Leonard’s frustrated arguing, as they do in this blooper. To start things off, they enter the hallway dressed up for a night on the town, heading toward Penny’s apartment. “Just for fun, let’s say I’m not,” Penny says. Leonard begins to explain the application process for the thing she’s complaining about, but Galecki can’t get through the speech without messing things up. “Before an application is released, they run …” he stammers and suggests they do it all over again, which leads to Cuoco breaking up laughing.

They retreat back to their first mark and end up starting all over again. And so, yet another argument between Penny and Leonard results in an emotional response — this time, one created of pure laughter. Is it any wonder “The Big Bang Theory” fans love this couple so much?

Here’s an announcement that would make Professor Farnsworth from “Futurama” green with envy — or at least keep him laughing hard enough to make sure he stays out of the Angry Dome. In this blooper, Johnny Galecki enters the room with a semi-extended tape measure while Kaley Cuoco sits on their couch, eating popcorn with a jug of water and a pile of fabric in her lap while waiting for her boyfriend to join her.

“Good news!” he exclaims before pausing. “Great news, not just good, great,” he says, correcting himself immediately and retreating to reset the take as Cuoco immediately bursts into laughter. It’s a quick slip of the tongue and an easy mistake to make, but it’s enough to make them both lose their composure — which is great news, indeed, for the studio audience watching live and any “Big Bang Theory” fans enjoying the show’s bloopers.

This is a mistake of a somewhat personal nature that’s still utterly hilarious. In this Season 10 blooper, Leonard is counseling Sheldon on how romance works, a plot conceit featured in some of the best Jim Parsons-related outings of “The Big Bang Theory.” “This is how relationships progress,” he explains. “You start with infatuation, but over time this is …” Johnny Galecki promptly stumbles on the rest of the line. The take ruined, he turns to Jim Parsons and says, “This is why I’m single at 41; I don’t know.” Parsons immediately chuckles, and the scene is reset.

While Galecki was, at the time, single in real life, he did end up finding true love. He married a woman named Morgan, and they are currently raising their daughter in Nashville, Tennessee. He also has a son from a previous relationship whom he co-parents. It seems love can find all of us, even if we sometimes have to take a few detours to get there.

You could say the cast of “The Big Bang Theory” captured lightning in a bottle with their antics, but sometimes it’s the simple shock of a misplaced word that makes them laugh.

To wit: in this blooper, Penny and Leonard are planning to share a romantic evening together. The lights are low, and there are candles flickering in the kitchen and living room. Leonard approaches Penny with a glass of wine in his hand, clearly hoping to evoke romantic memories of their shared past. “Hey, do you remember that time when we went wine tasting in Santa …” Before he can get to the “Rosa,” Johnny Galecki cuts himself off with a laugh and a quick “Sorry” that immediately cracks up Kaley Cuoco. Galecki then quips, “Remember when we went wine tasting right before the show?” “Yeah,” Cuoco retorts, chuckling. It’s a mistake, but it’s definitely not one to whine over.

Some actors love to try to save a take by ignoring the fact that they’ve managed to mess up a line. In this case, Johnny Galecki might have been trying to save Kaley Cuoco’s excellent delivery of her line by continuing after his own flub, but the cast can’t keep themselves from laughing.

Cuoco’s Penny is passionately defending the notion of friends teasing each other by busting their chops with insults and other jibes. “I’m saying that’s what friends do! They bust on each other! It doesn’t mean anything,” she exclaims. “I’m not surprised you should think so,” Galecki replies in character as Leonard, but he manages to mash up his words in the process and mangles his meaning. He pauses to wait for the next line, but Cuoco goes in for the kill. “You speak English?” she retorts. “I thought I could get away with that,” Galecki responds, sheepishly. “Nah,” several of his colleagues reply. Can’t blame a guy for trying.

Leonard didn’t only vent his frustrations regarding Sheldon to Penny. When Amy Farrah Fowler (Mayim Bialik) became a part of the cast, he sometimes turned to her to release pressure about Sheldon’s foibles. Unfortunately, in this blooper, his rant doesn’t come out quite as crystal clear as he intended.

“I know how to deal with Sheldon being Sheldon, but Sheldon being a rational, thoughtful person …” Johnny Galecki stammers. “Clueless!” he bursts out. As Bialik watches him struggle from her chair, she tilts her head in confusion, a smirk on her face. “It’s like when I …” Galecki tries to continue, but he’s unable to finish the sentence due to the odd look Bialik’s giving him. “What? You are looking at me like I’m crazy!” he says. Bialik cracks up, and the take is officially over. It’s clear that the two enjoy working with one another and got a huge kick out of the minuscule mistake.

We’re closing this list out with a double blooper in which Kaley Cuoco and Johnny Galecki manage to make a bit of a mess out of Leonard and Penny’s wedding. In the clip, the couple are in Las Vegas to tie the knot but are fighting over whether or not they should go through with the ceremony.

They’re talking things out while waiting for their number to be called when Leonard asks Penny, “And you promise you’re okay with everything from the car?” “Would you stop bringing it up?” she says. “Yeah, you’re sorry, I’m right,” Galecki responds — and quickly realizes that he misspoke. Cuoco immediately cracks up while he looks bashful, and she points a finger in his face. “That was so funny!” she gasps.

The second blooper clip picks up deeper into Galecki’s speech, and when he fails to get the word “about” out correctly, Cuoco cracks up. As she once again laughs and points a finger at her co-star, Galecki jokingly makes a break for the door.