Being There: The outtakes include several attempts to film the X-ray scene with Peter Sellers unable to speak his lines without bursting out laughing, made worse by the fact that the absurd questions had to be given with a deadpan, flat delivery by the character.
In the Caddyshack extras, Chevy Chase tells a story about Rodney Dangerfield getting increasingly distraught on set. When Chase talked to him between takes, Dangerfield said he was afraid he was ruining the film because he couldn't make anyone laugh and crew were walking away during his scenes. Chase had to explain that the whole damn crew was doing their best to not laugh and ruin every single take Dangerfield did.
Citizen Kane. Joseph Cotten stayed up 24 hours so that he could be believably drunk in one scene. When he says "film crimiticism", Orson Welles can't help but grin at the unplanned if realistic flub of the line.
Cloverfield. Just after the subway scene, when the camera is smudged, Hud is clearly grinning while he's cleaning it.
A famous example occurs in The Wizard of Oz. When Bert Lahr (the Cowardly Lion) makes his first appearance, Judy Garland (Dorothy) hides behind Toto. This looks like it's because she's frightened, but in actuality, she was just trying to cover up the fact that she was laughing at Lahr.
The reason why Wanda isn't onscreen much in the sex scene between her and Otto in A Fish Called Wanda is because Jamie Lee Curtis just couldn't stop corpsing, and eventually they just gave up and decided to only shoot Kevin Kline's face.
During the "baseball glove" scene in Good Will Hunting, Matt Damon was supposed to act stoic and introspective, but Casey Affleck's banter with Ben Affleck was so funny, they kept it. And the scene when Robin Williams is talking about his wife waking herself up farting has both actors breaking up laughing. If you watch closely during that scene, you'll notice a bit of shaky cam going on — the cameraman was laughing so hard that he couldn't hold the camera steady.
Peter Bull, playing the sombre Russian ambassador, is shaking with suppressed laughter at watching Peter Sellers's ad-libbed antics as he fights his Evil Hand. He was somewhat in the background, in the shadows, and regained his composure quickly after two or three seconds, so the scene could still be used.
One scene showing Bull ends just seconds from the actor corpsing as seen when his stoic façade cracks.
Another scene was not so lucky — originally the movie was to end with a pie fight. Seriously. Unfortunately, the characters had to be totally earnest about it to fit with the Black Comedy tone of the movie. That was a bridge too far; the entire cast corpsed within the first few pastry volleys, and the set (not to mention wardrobe) was too trashed for a second take.
Director Stanley Kubrick had so much trouble containing his own laughter on set that he would direct scenes by simply setting up cameras from every angle he could, then sitting against a wall on the far side of the set where his laughter wouldn't be heard in the film before calling action.
This was the biggest problem in filming The Fly (the original version, not this one), star Vincent Price couldn't help but laugh at co-star David Hedison's costume in the middle of filming, causing many takes to be cut.
Another Kubrick example is in Full Metal Jacket. At the beginning when Gunnery Sergeant Hartman is berating the men, Pyle begins to crack up. This was unintentional on Vincent D'Onofrio's part, but they kept going. This reaction is Truth in Television, as seen in the Real Life section below.
When David Cross's character offers J and K some mini-pizzas only for them to respond with unamused deadpan stares, Jones's mouth can be seen twitching as he struggles not to laugh.
In the Hilarious Outtakes, while shooting the car chase, director Barry Sonnenfeld kept referring to the automatic pilot actor as "Derek", which wasn't his name, leading Will Smith to say "Who the fuck is Derek?!", with Tommy Lee Jones and Rosario Dawson also corpsing with him.
In the dinner scene towards the end of Mrs. Doubtfire, Robin Williams is trying his very hardest to make Pierce Brosnan laugh- and you see at one point that Brosnan is at the breaking point.
In Austin Powers: The Spy Who Shagged Me, Dr. Evil calls Number Two out for his interrupting him during his evil plan explanation, asking him if he wants to run things and "wear the daddy pants". He then bounces a giant rubber ball representing Earth at his head repeatedly, taunting him the whole time. Despite the fact that Dr. Evil is making fun of him for crying, Rob Lowe is laughing throughout the entire scene.
The Marx Brothers: Groucho Marx was such a hilarious actor that Margaret Dumont could hardly ever keep a straight face when she was on screen with him. Groucho has this effect with other actors, some trying more valiantly than others not to laugh.
In Monty Python and the Holy Grail, watch Eric Idle as a peasant during the "burn the witch" scene. As Cleese stretches an awkward silence out further and further, Idle has to bite down on his scythe at one point to keep from laughing.
In Monty Python's Life of Brian, during the "Biggus Dickus" scene, the extras playing the guards were told that the scene would be serious and that they had to keep straight faces or they would be sacked. Michael Palin turned his performance up to eleven to get them to corpse (and even he can barely keep it together in some of the close-ups), and it ended up as one of the funniest scenes in the entire film. The characteristically deadpan John Cleese gets one scripted laugh in this scene, but exits before Palin really gets the guards rolling, leaving it undetermined whether he may have broken as well.note The story actually varies depending on who you ask, with some accounts varying from saying that the guards were actually aware of what was supposed to happen and were simply told not to laugh or smile until a certain cue, to the aforementioned threats of being sacked on the spot if they so much as smirked during the take. Regardless of which story, however, the reactions of the guards as they tried not to laugh as Palin did his damnedest to make them do so was genuine.
In Monty Python's The Meaning of Life, the oodles of kids from the "Every Sperm Is Sacred" sequence get an unrehearsed laugh from Palin by shouting "You could get them cut off in an accident!"
According to Cleese, Palin was "very naughty" on stage in his attempts to get the other Pythons to do this during live performances.
At one point during the live tour, Terry Jones and Graham Chapman decided to try and make each other corpse when walking on to do a sketch about pepperpots; since they did their makeup separately and came in from opposite sides of the stage, there was a ready-made battlefield. They gradually got more and more absurd with their makeup, climaxing when Jones (sporting a beard made entirely from lipstick) cracked up at the sight of Chapman with a circle of lipstick drawn around his face.
In And Now for Something Completely Different, Idle (as Arthur Wilson) is holding back a laugh when Sir George Head, O.B.E. (Cleese) takes out a dictionary to look up the word "mountaineer" in the Climbing Mt. Kilimanjaro sketch.
During the (not kidding) twenty straight minutes of rock climbing in B-MovieLost Continent, as Cesar Romero is pulled up a cliff, his trousers begin to slide down and the actors hoisting him grab him by the back of his belt to prevent it. Behind them, Hugh Beaumont is visibly snickering at this and making a half-hearted attempt to hide it.
A bit of corpsing gets through in Spaceballs, but only slightly. When the Radar Officer tells Dark Helmet, "I'm having trouble with the radar, sir," there's a bit of a chuckle at the end. It should be noted that the officer was played by Michael Winslow, the man of ten thousand sound effects. Almost a dozen Police Academy movies and this was the point where he almost loses his composure? Hilarious. (You can also see him covering his mouth as Helmet proclaims the jam to be "Raspberry!")
A more obvious bit of corpsing happens in Blazing Saddles when the Waco Kid (Gene Wilder) gives his "common clay of the new West" speech, then Wilder ad-libs, "You know...morons." Cleavon Little (Sheriff Bart) bursts out laughing at that point, but they decided to leave it in.
Dee Wallace (Elliott's mother) in E.T. the Extra-Terrestrial has to stifle an out-of-character laugh as she begins to scold him for calling his brother "penis breath" at dinner, suggesting the insult was ad-libbed.
According to Chris Columbus, the first Potter film is filled with rapid cuts to compensate for how often the child actors would smile or laugh in the middle of takes. Rupert Grint was known for being especially bad for corpsing and apparently, he didn't get much better when he grew up.
During The Order of the Phoenix, an instance of corpsing became a Throw It In! (when the Trio all laughs after Harry talks about his kiss with Cho). Daniel and Rupert chuckled at Emma's line "just because you've got the emotional range of a teaspoon", and Emma soon followed suit.
Emma Watson herself revealed that her scenes in movie seven with Rhys Ifans, who plays Xenophilius Lovegood, were especially prone to this. According to her, fans nicknamed her "Giggles" since she, in her own words, was "so bad" at keeping a straight face. It was also the first and only time in the entire series that Emma received a "red card", meaning that as in football/soccer, she had to be sent off-set to calm down.
In Ghostbusters, when the gang goes to the Sedgewick Hotel and speaks to the man by the elevator ("What're you supposed to be, some kinda cosmonaut?"), you can see Dan Aykroyd (Ray Stantz) turn his head and look down at Bill Murray's (Peter Venkman) comments about roaches. ("Must be a big cockroach." "Bite your head off, man.") Justifiably understandable, because the "Bite your head off" line was improvised right there and then, so nobody saw it coming at all.
Lindsay Lohan and Rachel McAdams have both said publicly that the filming of Mean Girls was often prolonged by fits of giggles induced whenever Tim Meadows was on set. It apparently became his mission for the duration of his work on that film to make Lindsay laugh on-camera as often as possible.
Meet the Parents: Ben Stiller's "kung fu grip" remark on the airplane causes an extra to laugh and duck out of sight so as to not ruin the take. He's seated near the back in case you're looking.
Courteney Cox tries and almost succeeds in looking solemn when "Larry" (Jim Carrey) acts out "a button-hook pattern in super slo-mo". She nearly cracks when he does an "instant replay" and "bounces" off the doctor's shoulder. Additionally during those scenes, when Ace slams his head into a chair after drinking from a fountain, if you look closely, the doctor with Courteney can be seen chuckling.
You can also see Tone Loc trying not to crack up during the ass-talking scene.
In the sequel, Ian McNiece is just barely holding it together during Ace's shadow puppets routine.
Watch and count the number of scenes where Gene Wilder is inches away from completely losing it. Igor's "take the bags" scene had to be filmed multiple times — not because the cast corpsed, but because the crew was laughing so hard that it was messing up the takes.
The scene with Gene Hackman was supposed to be a one-day shoot; between the cast and crew, the scene took nearly a week to film due to corpsing.
A chronic problem on the set of Abbott and Costello Meet Frankenstein, and indeed, Lou was infamous for going out of his way to crack up his costars, both with his performance and with unexpected pranks. The scene where Lou sits on Glenn Strange's (the Frankenstein monster) lap had to be reshot so many times that even Lou lost his patience. Strange replied: "I can't help it. Somehow I can tell just from the back of your head what you're doing up there." Even in the finished scene, you can observe the corners of Strange's lips twitching.
In Star Trek (2009), Simon Pegg (Scotty) ad-libbed the line "can I get a towel" during his character's first meeting with Spock. Although they decided to keep the line, they had to re-shoot the take because both Zachary Quinto (Spock) and Chris Pine (Kirk) started laughing, and they couldn't save the take (the original can be seen in the blooper reel). Even in the final take, if you look carefully, it's clear that Quinto is having to work at not cracking up again.
In Star Wars: A New Hope, you can see Harrison Ford grin and look away from the camera to hide his amusement when he says "We're all fine here now. How are you?" over the radio in the detention center. You also briefly hear his voice crack from trying to hold back laughter when he quips "large leak, very dangerous!" Notably this was because he had actually forgotten his lines and was just improvising — he was laughing (and somewhat embarrassed) because he was certain they were going to cut when instead they kept going.
In The Empire Strikes Back, after Lando flirts shamelessly with Leia and an annoyed Han says "All right you old smoothie" you can see Carrie Fisher break character and grin. According to Fisher herself in an audio commentary, this was aggravated by the previous night, when Eric Idle (at that point filming Monty Python's Life of Brian) had held a party, with a drink he called "Tunisian Tabletop Cleaner". The resulting buzz apparently lasted well into the following day's filming, giving everyone on set a tendency to sport a big grin.
In Rogue One, Alan Tudyk improvised K2-SO slapping Cassian in the face - and as a result, while Cassian appears to be in pain, the Face Palm is Diego Luna hiding his laughter. (director Gareth Edwards also said Tudyk making him laugh was not easy for him, as he had to bite his lip hard to prevent the handheld camera from shaking).
In Sister Act, when Mother Superior is raging at Deloris for turning the choir into a sideshow, the priest knocks on the door. Maggie Smith literally squeaks a loud "Come in!" that is so out of character (both for Mother Superior and for Maggie Smith) that you can clearly see Whoopi Goldberg immediately cover her mouth as she starts corpsing.
The Blu-ray release of X-Men: Days of Future Past includes a deleted scene along with a few takes that went wrong because while filming it, Singer had injured his vocal cords and "sounded like Mickey Mouse", so everyone (especially Jennifer Lawrence) couldn't stop laughing at him. It didn't help that Lawrence's line was "You're living a fantasy world!"
Watch Mark Ruffalo in the infamous shawarma scene of The Avengers's second Stinger; Chris Hemsworth can be seen briefly smiling when he sees Ruffalo holding back laughter. Also, in the bloopers, this happens to Tom Hiddleston/Loki while he's trying to film his pained reaction to being beaten up by the Hulk.
In Guardians of the Galaxy, the Broker tries to explain to Yondu why he can't help him find the Orb, only for Yondu to belittle him by interrupting him with gibberish and babbling. Kraglin could be seen behind him, trying (and failing) to contain his laughter.
Avengers: Age of Ultron, has an in-universe example. The team was just attacked by Killer Robots and is demanding an explanation from Tony... who breaks into a nervous giggle fit. He takes a minute to compose himself, even as Bruce gives him a Dude, Not Funny! warning glare.
The "wanna hear the most annoying sound in the world" scene from Dumb and Dumber was not in the script; it was ad-libbed by Jim Carrey. In the final product, you can see actor Mike Starr (who plays the hitman Mental) visibly trying not to laugh. Jeff Daniels starts corpsing too, briefly before the camera cuts to a close-up of Starr.
Lost in Translation features a scene with Bill Murray "talking" to an elderly Japanese woman in a hospital waiting room. Nearby are two extras who are nearly bursting from trying not to laugh. Murray appears to notice them and goes even further trying to provoke a reaction from them.
So I Married an Axe Murderer has a scene where Mike Myers (as the father of his other character in the movie) tries to teach Anthony LaPaglia's character about a secret society known as "The Pentaverate", but quickly goes off topic and starts ranting about Colonel Sanders. LaPaglia manages to hold it together for his one line, but that's about it. There's also a scene where the same character is making fun of the large head of a kid, and LaPaglia tells him to be nice, while visibly laughing. Clearly, the director decided to Throw It In!.
Murphy was apparently the cause for plenty of this in Beverly Hills Cop, especially because most dialogue was improvised. A good example is the "Super Cops" scene: John Ashton is doing sort of a Face Palm to hide his laughter. (Judge Reinhold, in turn, was pinching his thighs through his pants pockets.)
In The Golden Child, when Kee Nang drags off Chandler Jarell in the airport scene, Charlotte Lewis is very visibly on the edge of bursting into laughter.
The scene in The Princess Diaries where Mia slips and falls off the bleachers was not scripted and was a complete accident but the director kept it in anyway. Heather Matarazzo breaks character briefly but Anne Hathaway is too busy laughing her head off (which is in character) to affect the scene.
Richard E. Grant broke into laughter delivering his line about putting a jukebox in the Penrith tea rooms in Withnail and I but since he and Paul McGann's character were supposed to be drunks it was kept in.
Robert Downey Jr. had a quick moment in Tropic Thunder where he breaks into a grin after his "Book-script" line before snapping back into a stare.
Tom Hanks was asked to do this with one of the child actors in Apollo 13 because they were getting a bit bored. Mary Kate Schellhardt (Barbara Lovell) was previously in Free Willy 2, and Hanks used this to his advantage. He, as Lovell, started talking about the astronauts' freeze-dried food and then suddenly switched to "No, it isn't...that's...that's *whale*! It's a 'Free Willy' sandwich!"
A common hazard in most of Christopher Guest's films; due to the almost entirely unscripted nature of the films, combined with the cast being some of the most talented comic actors in the business. In A Mighty Wind, the cutaway immediately after Michael Hitchcock Dope Slaps an increasingly annoying Bob Balaban was necessitated by the entire cast and crew exploding into laughter.
In Hitch, watch Will Smith's expression during the "dance lesson" scene. He covers his mouth through the entire sequence, and when you see Kevin James's (incredibly nerdy but excellent) dancing, it's easy to guess why. One of the DVD outtakes shows Smith erupting with laughter the instant "Cut!" is called.
Watch Christine McIntyre during Shemp's "death" scene during The Three Stooges short Who Done It. She's obviously struggling to keep her composure during Shemp's seizures.
In this scene from Back to School, the script called for Jason to sit quietly and look disgusted at his dad's secretary taking notes in class, but actor Keith Gordon simply could not stop cracking up on-camera at actress Edie McClurg. They decided to Throw It In! since it works just as well that Jason is laughing in frustrated disbelief instead.
In UHF, when Billy spits in Uncle Nutsy's face, you can see the child actor start to crack up as his loogie hangs perfectly from Weird Al's nose.
The Belching Contest scene in Revenge of the Nerds, keep an eye on John Goodman as the coach. He keeps studying his shoes while simultaneously making sure his hat doesn't come off, all to keep from laughing out loud on camera from the antics of actors Donald Gibb and Curtis Armstrong.
Birdemic. Poor Whitney Moore, who played Nathalie, knowing she was in an awful movie, said almost every line with a giggle.
Matthew Broderick did a heroic job keeping a straight face around Jim Carrey in The Cable Guy, but simply couldn't do it during the chicken skin scene at Medieval Times.
At one point early in White Christmas, Bing Crosby and Danny Kaye dress in drag and perform an act lip-syncing to a record of the female leads singing. While Danny keeps a straight face all the way through, Bing repeatedly flubs his lip-sync and almost cracks up, especially when Danny hits him in the face with a feathered fan. It works in context since the characters were supposed to be improvising an act to keep the police distracted while the singers escape out the back, and apparently it was filmed all in one take with only minimal rehearsal so it wouldn't look too polished.
During the soap poisoning scene, every time the Old Man and Ralphie's mom duck their heads into their hands or bury their faces into Ralphie's chest/shoulder, it's to hide their uncontrollable laughing, when they were supposed to be sobbing uncontrollably.
Happens again when the father is trying (and failing) to repair the leg lamp. In the background the mother covers her mouth to hide the big smile and how she's on the verge of cracking up.
Melinda Dillon can't stop laughing through the entirety of the Chinese restaurant scene, as they hid a lot from her what they were planning to do. She's visibly breaking when the waiters try their hand at singing "Jingle Bells" and howls in laughter and can't stop when they bring out the duck and where the gag goes from there.
In Wayne's World, a famously ad-libbed scene between Wayne and Garth takes place as the two of them rest on Wayne's car, watching airplanes take off. Dana Carvey (Garth) can briefly be seen snickering to himself as he suddenly thinks up the line, "Did you ever think it was attractive when Bugs Bunny dressed up as a lady bunny?". Mike Myers (Wayne) manages to stammer out "No...!" while desperately trying to hold a straight face, before completely losing it and cackling madly. The reaction was so funny, the creators decided to leave it in the final cut.
Fat Slags: Dolph Lundgren is obviously trying not to laugh when the slags give him mouth-to-mouth.
Count Yorga: In the scene where a newly vamped Erica and fellow vampire bride running into Yorga's throne room to attack Micheal. You can see Erica's actress, Judy Lang, laughing a bit. Helps with the scene though to show her newfound bloodlust. Ironic too since Erica's now a vampire, she's a literal walking corpse.
In Dracula: Dead and Loving It, during the scene where Harker and Helsing stake Lucy. Steven Weber, who played Harker, was told that he was going to be sprayed with fake blood, but nothow much. So when he starts driving the stake in and is hit with it, he's clearly struggling not to laugh when Helsing tells him to hit her one more time to be sure only to refute "She's dead enough!".
When filming The Sound of Music, Julie Andrews couldn't resist giggling during the "Something Good" number, as the arc lights made noises that sounded like someone Blowing a Raspberry. Director Robert Wise decided to film Andrews and Christopher Plummer in silhouette to hide her laughter. Some of her chuckling can still be heard in the final film, though it at least occurs at times that make sense for the context.
In Plan 9 from Outer Space, when Eros' actor delivers the infamous "Your stupid minds! Stupid! STUPID!" line, you can notice Tanna's actress barely managing to hold back her laughter. Earlier in the film, when zombie Tor Johnson attacks Eros, Tor can be seen straining to maintain his stone-faced expression as Dudley Manlove furiously overacts.
In The Fifth Element, during the scene in which Korben outwits the drug-starved mugger at his apartment, Bruce Willis suffers a clear moment of genuine amusement at the mugger's hilarious acting and ridiculous hat, his serious face cracking into a wide smile as he barely keeps himself from laughing out loud before regaining his composure enough to say, "That's...a very nice hat." (Given that he's dealing with an inept burglar...) Later in the movie, when Chris Tucker starts singing "All Night Long," you can see Willis visibly struggling to keep a straight face in the background.
Billy Crystal was incorrigible during his filming of The Princess Bride, as most of his dialogue as Miracle Max was improvised, meaning that Mandy Patinkinnote who actually bruised a rib by trying to hold in his laughter and especiallyCary Elwes (seeing as he was supposed to be mostly dead) had to work hard to keep from corpsing. Director Rob Reiner couldn't even be on set during the Miracle Max scene because his laughter was ruining takes and had to watch from a monitor in a separate room.
In National Lampoon's Christmas Vacation, when Ellen's mother tells her that she has haemorrhoids Beverly D'Angelo can briefly be seen struggling to keep a straight face.
In Deadpool (2016), Gina Carano can be seen struggling to keep a straight face when Negasonic Teenage Warhead is completing a tweet before the final battle.
By the same token, Negasonic's own laughter earlier on when Deadpool tries (and fails, miserably) to beat up Colossus is probably very genuine.
In The Wolf of Wall Street, as Donnie has to deliver a briefcase to Brad (and the latter is arrested), Jonah Hill is clearly pushing Jon Bernthal to the extreme, and Bernthal can't hold his laughter as he hears "Oh my God, the emperor of Fucksville came down from Fucksville to give me a pass!"
In Dungeons & Dragons (2000), when Jeremy Irons as Profion goes, in typical Large Ham fashion, "My destiny!", you can see Bruce Payne (Damodar) desperately try to contain his laughter. It's priceless. Minutes later when Irons says "Let their blood rain from the sky!", he clearly is laughing while he says it.
Payne is also clearly struggling to keep a straight face during the "do not let them escape" scene. At least somebody had a good time with this movie.
An In-Universe example occurs in Revenge of the Pink Panther. Dreyfus is giving his eulogy at what appears to be Inspector Clouseau's grave. He cries to cover up his Corpsing, and is only barely successful.
In Speed, during in the infamous cradle scene, you can hear Keanu Reeves trying hard to contain his laughter in his voice as Sandra Bullock panics at the thought of hitting a baby and having to reassure her it was just cans.
Averted by editing for Alien: Resurrection. The blind, one-handed, over-the-shoulder basketball shot that Ripley makes wasn't clever editing or special effects; it took six takes, but Sigourney Weaver made that basket entirely on her own. However, Ron Perlman was so astonished that she actually did it that he instantly, visibly and loudly reacted without thinking, nearly ruining a perfect take. In the finished film, the scene switches to a different camera angle a split second after Ripley makes the basket, just barely managing to cut out Perlman's reaction.
In-Universe, in the film Florence Foster Jenkins, Jenkins' accompanist Cosme McMoon is caught off guard when he first hears Florence's Giftedly Bad singing and tries desperately to hold himself together and not laugh. He succeeds but just barely, finally bursting into hysterical giggles when he makes his escape into the elevator. Agnes Stark is less successful at Florence's debut concert, falling over laughing and feebly trying to pass it off as a "coughing fit."
In-Universe in Justice League (2017), as Aquaman starts doing some Brutal Honesty confessions and the others struggle not to laugh... until they decide to point out he's accidentally wrapped in the Lasso of Truth.
In-Universe in the first Police Academy. After the horse incident with Harris what Mahoney witnessed, he asks Mahoney in the next scene if he had mentioned it to anyone. Mahoney denies it, but everyone else starts snickering as soon as Harris walks past them.
In Napoleon Dynamite, when Pedro's cousins scare off the bullies who were trying to take another kid's bike, said kid is very clearly cracking up at the end of the scene.
In Kick-Ass. When Mark Strong, as mob boss Frank D'Amico, is talking to the driver in the car, in one of the early scenes. He's describing the specifics of the slushie he wants, and you can clearly see Christopher Mintz-Plasse (sitting next to him) is about to crack up as Mark Strong plays it totally deadpan.
The early Charlie Chaplin installments show some cases of this, as Silent Comedies of the 1910s had a tendency to throw things in as they came along. In the 1915 Movie A Woman, Chaplin shows up in drag, and when Edna Purviance first sees him like this, she cracks up so hard she has to sit down on the floor. The take was kept in the final edit of the movie.
It's a Wonderful Life: When a crew-member dropped some props during filming, resulting in a clattering crash, Thomas Mitchell ad-libbed the line "I'm alright! I'm allllrright!" from offstage, causing Jimmy Stewart to crack up. Since it was an appropriate reaction for his character, it was included in the film.
Towards the end of Good Burger, the two have become Fire-Forged Friends and Dexter decides to rip up the contract he tricked Ed into signing that is effectively scamming him out of money, only for Ed to ask if the reason the partnership is ending is because he's Black. As anyone who's ever seen All That could tell you, Dexter's very genuine laugh and stammered reply is clearly Kenan Thompson cracking up at Kel Mitchell's response.
Talladega Nights: The Ballad of Ricky Bobby: In the ending credits, we get to see just how much improv humor all the actors have, and the outtakes are at least as good as the rest of the movie. While both John C. Reilly and Will Ferrell make mock commercials that are brilliantly hilarious and wind up corpsing themselves — especially when talking about packs of wild dogs — they also show outtakes from the hospital scene where Will Ferrell is lying in bed. Michael Clarke Duncan gets in a brilliant attempt to corpse Ferrell by talking about dressing up like Donna Summers... and then begins singing Last Chance. It succeeds flawlessly.
Considering how much this French actor considered humour Serious Business, it was extremely rare for De Funès to crack up at his own jokes. However, there's an infamous instance during the filming of The Sucker: the Citroën 2CV driven by Bourvil's character is hit by Mr. Saroyan's Rolls Royce, which causes it to fall into pieces à la Blues Brothers. Both drivers then proceed to have an argument over the wreckage, during which Bourvil threw the ad-libbed line "Maintenant, elle va marcher beaucoup moins bien, forcément!" ("Now, it will run a lot less well, naturally!"). De Funès had to lower his head to hide his snicker at the unexpected reply in order to not ruin the shot. (Which they couldn't afford, as they had only one self-destructing car available...)
His co-stars, now on the other hand... they found it very hard to resist cracking up to his frequent grimaces (sorry, expressions). Especially since he loved having an audience, a habit he got from theater.
When filming the 1974 version of Death on the Nile, Olivia Hussey and David Niven found they couldn't get through their scenes together without bursting out laughing. They had to work out an eyeline so they wouldn't look each other in the eye when they had to say lines to each other - looking at the forehead for example.
In Fast & Furious 6, when Hobbs arrives at the barbecue, Roman remarks in a sing-song tone that Mia "better hide the baby oil", to which Hobbs instantly replies in the same tone with "you better hide that big ass forehead", followed by Tej immediately spitting out his beer. That Spit Take by Ludacris was genuine, as was Tyrese Gibson being at a loss for words, because Hobb's line was improvised by Dwayne Johnson.
In Sonic the Hedgehog (2020), you can see Agent Stone struggling not to laugh the entire time Dr. Robotnik is brow-beating Major Bennington while the major just tries to get a word in. It's hidden quite well by some cuts, but you still see Lee Majdoub shifting on his feet, the occasional smirk, and finally ducking out of frame to hide the grin he can't hold back anymore at the "nobody cares" rant. You can see the whole thing here.
On the DVD extras for The Apple Dumpling Gang, Tim Conway and Don Knotts tell the story of having been given three days off to work out the choreography of the scene where their characters steal the ladder from the firetruck inside the firehouse. They used the time to play golf instead, didn't discuss the scene at all and made it up as it was being filmed. Apparently they were so good the director had no idea they hadn't practiced. The only other actors in the scene are a sleeping fireman and a dog, who watches them with interest. The actor playing the fireman kept peeking and finally cracked up (off camera, but the audio picked him up) - if he hadn't lost it, they've have been able to film the whole scene in one take. As it was, they did it in two.
The Birdcage: During the scene where Armand, Agador and Val argue in the kitchen about Agador not preparing an entree there's a moment where Armand stumbles and nearly falls over. This was a mistake by Robin Williams, who managed to stay on his feet but is clearly struggling not to laugh for the rest of the scene.
Helge Schneider often doesn't even try to keep himself from corpsing in some of his films. A notable example is the boot-crapping instruction scene in Texas - Doc Snyder hält die Welt in Atem in which he suddenly starts laughing, as does the actor he is talking to. It doesn't really help that the dialogs are more ad-libbed than scripted.
The In-Laws: Alan Arkin admitted during the scenes with Sheldon, Vince, and General Garcia, you can see him come very close to doing this, and he had to put his hand over his mouth to avoid laughing on camera.
You can obviously see Tommy Lee Jones struggling to keep from laughing on camera. He's only partially successful. (Quick smile at about 44 seconds in.)