Guilt by Association Gag

Geoffrey: How did we all die at the same time?
(The Grim Reaper points at one of the platters on the table.)
Grim Reaper: The salmon mousse.
Geoffrey: Dearest, you didn't use canned salmon, did you?
Angela: I'm so dreadfully embarrassed!

Lady Presenter: (much later, as they're all being carried away to the afterlife) Hey, I didn't eat the mousse!

—Monty Python's The Meaning of Life

In a comedy, when a bunch of characters are subject to some kind of punishment or awful revenge, there will often be exactly one character who doesn't deserve it. No matter how much this character voices his objection, he will never be recognized as an exception. He must suffer with everyone else.

Compare: My Friends and Zoidberg, Can't Get Away with Nuthin', Go Among Mad People. If the character didn't do the listed thing, but DID do something else, may become I Take Offense to That Last One. Jokes of this kind are a type of Black Comedy.

This trope is NOT just any group of people where one person doesn't belong in the group for whatever reason.

Examples of Guilt by Association Gag include:

Anime

• Mahou Sensei Negima has one of these during the "Kiss Negi" competition during the class trip. Nitta tells the students that anyone caught outside their hotel rooms will be forced to do the Seiza Squirm in the lobby all night. Chisame is roped into the competition by Ayaka, realizes early on the whole game is stupid, heads back to her room. And is caught by Nitta on the way. Eventually everybody else is caught too...along with Negi, who had absolutely nothing to do with it (but he was also outside of his room, for different reasons). This makes even less sense when you consider that a teacher, 10 years old or not, really should be able to be out of his room.

Comedy

• In that Eddie Izzard routine, the guy who accidentally asks for death instead of cake, even though he meant cake.
• The last victim of the guillotine in this sketch courtesy The Whitest Kids U' Know

Comic Books

• Throughout Arkham Asylum: A Serious House on Serious Earth Professor Milo appears in the background, calmly and rationally explaining how he is not insane and does not deserve to be in the asylum.
• A rare serious example: in Maus, the punishment comes from the Nazis towards a prisoner who may or may not actually be the race they claim he is. Every day at lineup, he desperately insists that he was a German soldier who doesn't belong with "these Yids and Polacks". This is emphasized when Vladek sees him as a cat (analogous to a German) but the other Germans see him as a mouse (analogous to a Jew.)

Film

• The titular death scene from The Meaning of Life. It was, in a rare case for Monty Python, an ad-lib. What made that particular scene even funnier is that the character sounded more excited than anything, since they were in the middle of an intellectual debate about the afterlife when Death arrived.
  • Another Monty Python example occurs in Life of Brian, during the crucifixion march scene. A kindly onlooker who tries to help a fallen prisoner by lifting his cross is marched off to the execution site by the guards after the prisoner ditches him and runs off into the crowd. This may be particularly savage Take That at Simon of Cyrene.
  • Monty Python just loves this one—near the beginning of Monty Python and the Holy Grail, a man is loaded onto a cart full of dead plague victims. When he insists he's "not quite dead yet" and attempts to leave, the cart-pusher refuses to take him at first, but the man who brought him slips the cart-pusher some money. A hefty whack from his cudgel and the man wasn't complaining any more.
• Narrowly averted in Dogma, when the two angels Loki and Bartleby slaughter the whole board of directors of a fictional corporation, for "raising an idol (a cartoon character) that draws worship from the lord..." They had all also committed other, horrible sins to deserve their punishment. The only one who was spared was the sole woman among them, who had committed no sins... though Loki still almost killed her because she didn't say "God bless you" when he sneezed. Bartleby stops him at the last moment, but only because he's tired of waiting.
• In Chicago's "Cell Block Tango," five of the six women insist their victims "had it coming" while not accepting responsibility. The sixth protests that she is innocent; unfortunately, in Hungarian. She's the one who ends up being executed.

Live Action TV

• On Arrested Development, Oscar is constantly being hunted down and savagely beaten by police (and was actually imprisoned between the second and third seasons) for the crimes committed by his identical twin brother. It's especially ironic because he's probably the only member of the family who hasn't committed massive fraud and "...maybe a little light treason"; he never seems to be guilty of much beyond possession of marijuana.
• One episode of Father Ted features Ted and Dougal sneaking around after dark in a "rest home" full of sick and/or demented priests; the inmates all loom out of the darkness spouting deranged gibberish, except for one poor guy who enunciates quite clearly: "I really shouldn't be here!". He is of course left to his fate.
• Non-Comedy example: In Ashes to Ashes the cops suspect someone protesting about the Docklands redevelopment might try something on the Royal Wedding day, so he rounds up members of the protest groups, and one man from the Anti-Nazi League by mistake; he gets the worst of it because he talks back.
• Mike grew up in the 80's; Space Mutiny was made in the 80's; Therefore:

Tom: "Okay, okay, Mike, be honest with us, this music really kinda gets your blood pumping, right?"
Crow: "Yeah, Mike. This is your music done by your people, so I blame you for this entire movie."
Tom: "Yeah, it's just like you to make a movie like this. Tsh."

Web Animation

• The Demented Cartoon Movie: "GAAAAAAH! Even when they fix the whole thing with the Zeeky Words, it still blew them up!"

Web Comics

• In Eight Bit Theater, the Light Warriors are all to be killed by Sarda because they're horrible people. Except for Fighter. "He's a casualty."
• in Drowtales, this winds up happening to Kyo'nne, who seemed to think she'd get off easily because unlike her friends she wasn't tainted. They capture her anyway for being "corrupted", literally guilt by association, and would have "cleansed" (read: brainwashed) her if Chirinide and Shan'naal hadn't interfered.
• Greg becomes the target of Ted's ex-girlfriend's homicidal rage as Ted manages to escape, leaving Greg to fend for himself. Although he has never met her, the guilt has already been transferred.

Western Animation

• Futurama:
  • In the episode "Fear of a Bot Planet", Leela objects to being sentenced as a human by the human-hating robots because she is a one-eyed alien. (Although before going, The Professor did warn her that the robots are "not fans" of humanoid aliens.) Turned out much later that she actually is human, albeit a mutant one.
  • Then another time Leela got fired with Fry and Bender when the two took the ship out for a joyride around the world with the Planet Express building tethered to it, but she did leave the key in the ignition.
• In Metalocalypse, Toki is often the one who doesn't eat the mousse. One of his catch phrases is even "Evens Toki?" When Dethklok comes out with a line of clothing, their humanitarian fashion designer berates and abuses them all for not being in shape, including Toki, who is in great shape and who didn't lie about his measurements. (At least his new clothes fit perfectly.)
• The Simpsons: in the "Heck House" segment of episode "Treehouse of Horror XVIII", Bart, Milhouse, Nelson and Lisa are sent temporarily to hell, yet Lisa took no part in the chaos they wreaked. She points this out along the way to hell: "I warned you, and yet my punishment is no less severe. That's odd".
  • In a different episode, "Simpsons Bible Stories", ends with the Rapture. The Simpsons are to be sent to Hell...except Lisa, who is pulled heavenward in a beam of glorious light. Disturbingly, Homer is able to reach up and pull her down to hell with them saying "Where do you think you're going, missy?"
  • In another episode, "Grade School Confidential," Martin Prince's parents throw him a birthday party...but they serve raw oysters instead of cake. The children all come down with food poisoning. Including, at first glance, Lisa (a vegetarian). However, it's a subversion in that she only pretended to be sick so she wouldn't have to stay at the disaster of a party.
  • In yet another Halloween episode, everyone in town is cursed by a witch, causing them to turn into their Halloween costumes, including Hans Moleman, who turns into a mole despite not wearing a costume.
• Edd from Ed, Edd 'n' Eddy doesn't deserve most of the crap he goes through even though most of the time he does nothing wrong, he gets beaten up on a fairly regular basis along with Ed and Eddy whom most of the stuff that happens is their faults, mostly Eddy though. This was Lampshaded on one occasion after beating up the Eds Sarah admits that Edd didn't deserve the beating but then she adds "Give those cute ones an inch, and they'll take a mile!"
• The Hey Arnold! episode where a drill sergeant replaced Mr. Simmons. He punished 3 kids by making them stand in room's corner. He makes Stinky do the same because of "symmetry".
• In one episode of The Grim Adventures of Billy and Mandy, a phantom duck caused many people to get arrested, including Hector Con Carne who stated "I'm not even on this show anymore!"
• Happens in American Dad, when Steve is targeted with his other friends, who misled him into believing three of the Alpha Bitches sabotaged girlfriend Debbie's chances for election, leading to some Misplaced Retribution. Steve apologizes and reveals it was his friends, but he gets targeted along with them.
• In one teaser of an episode of Batman the Brave And The Bold, the sidekicks were forced to fight a training simulation as punishment for fighting each other. Speedy was one of them even though it was Robin and Aqualad who fought each other.

Real Life

• Schools often employ this tactic to keep students under control in chaotic classrooms, much to the chagrin of well-behaved students. In more recent years it's become something of a Discredited Trope, as teachers have gradually come to realise that the badly-behaved students often enjoy getting their more well-behaved peers punished for no reason, and can actually cause the ones who normally behave to start being disruptive themselves once they realise they're going to be punished either way.
• This can be used as a punishment in military training, and can and has been exaggerated to the point of only one person "eating the mousse". This can have the intent of banding the group together against an unfair superior or of having the group further punish their guilty peer and leaving the guilty party an outcast for at least as long as they continue to misbehave. Whichever result is intended can, of course, backfire into the other result.