Basically this is when one character is sleeping with another's mom, usually for comedic effect.
Often carries the implication (if it's not stated outright) that the speaker was able to sleep with the mom because she Really Gets Around, usually prompting an angry My Girl Is Not a Slut reaction. Reactions are especially volatile if the mom has only recently become divorced/widowed from the dad, and especially if she's still married to him. The characters this is said to are usually male, and they almost never get similar remarks about their dads; possibly a result of Most Writers Are Male.
People seldom say "Thank you, man, she was so lonely after the divorce" or "I hope you had fun, and I'll kick your ass if she didn't" or "Well I hope you enjoy genital warts". Any of these would destroy the insulting intention with a good shrug-off. Strangely, often the only proof is the word of the person who says the line, and few of the attacked ever seem to seriously doubt the sentence. This trope is common mainly in American media, rarely seen (if at all) in continental European or Asian media (at least for comedic effect, it is seen for tragic effects in the form of rape, but then it's not this trope).
If it's just an insult - they never actually did it - check out Your Mom. note Everyone else has!
"I banged your wife" is a variant, and much more insulting. If it happened a long time ago and said character was conceived from said coitus, see Luke, I Am Your Father.
Johnathan Glenn from Brain Powerd twice over, leading to this joke among fans of the show:
Johnathan: I did your sister.
Yuu: You motherfucker!
Johnathan: Yeah, her too.
Not played for laughs in Revolutionary Girl Utena, where Akio sleeps with his fiancee Kanae's mom in a sick game of manipulation and guilt tripping.
In Chiho Saito's Kanon, which may or may not have inspired the aforementioned Utena example, Gen Mikami is sleeping with his fiancée Maria's mother. When Maria finds out about this affair (shortly before the wedding, no less) she goes more than a little nuts.
"Harry Potter and the Sun Source" by Clell65619 has Harry do this to Narcissa Malfoy in Chapter 6. Raised by Master Chiun of Sinanju in the "Remo Williams" universe, Harry is an assassin who killed Lucius Malfoy during an attack. Going to Malfoy Manor on Boxing Day, he guesses Narcissa wants Voldemort dead so Draco won't get further infected by his evil. Her offer to "ensure a more binding agreement" leads to Draco seeing them in the bedroom and Harry zinging Draco with "Don't worry Draco, you won't have to call me 'Father' right away. We'll work into it." Needless to say, this doesn't end well for Draco..
The film Mister Woodcock has a torturous gym teacher who inspires a fat kid to become a self help mogul, and then we find out he is banging his mom. Over, and Over and Over again.
Guy: "If I had fought you when you were still capable of making bastards..." Godfrey: "I knew your mother when she was making hers. Fortunately you're too old to be one of mine."
Henry Fool: "I made love to your mother about half an hour ago, and now I'm beginning to think that maybe it wasn't such a good idea."
In Face/Off, Castor Troy casually taunts Sean Archer by mentioning that he enjoys "boning [Sean's] wife".
It's not just limited to Archer's wife Eve. When Archer first goes undercover as Castor, he gets attacked in prison by a husky Russian, Ivan Dubov, who wants revenge on the real Castor ever since Castor had three-way sex with his wife and sister.
In Ken Park, one of the characters has sex with his girlfriend's mother.
In Major League, Jake comes out to the mound at one point, and Rick admits that his arm is worn out and he doesn't know if he can get the last batter out to win the game. Jake tells him to get it over the plate, and then proceeds to describe the wife variant - in detail - to the batter. Said batter immediately pops up, slams his bat on the ground angrily, and can do little as Jake catches it for the last out of the game.
Touched upon but never really gone into in much detail in Wicked Lovely: Aislinn's mother was previously thought to be the summer queen, prior to her suicide and Aislinn's reveal as said queen. This means that she had a relationship with Keenan. Whom Aisliin breifly falls in lust with in Fragile Eternity. It was non-sexual in both cases, but the squick is still there.
In the Red Dwarf episode "Polymorph", the Polymorph takes on Rimmer's mother's form and claims to have slept with Lister just to elict outrage from Rimmer - so it can devour his anger. (Rimmer's mother had this sort of reputation anyway, Rimmer was just in denial.)
And, of course, there's Mother Lover, although that one differs from most examples in that everyone involved seems more than okay with the arrangement.
Sean Connery (Darrell Hammond) often tormented Alex Trebek (Will Ferrell) in the Celebrity Jeopardy! skits by using various forms of these jokes.
In the My Name Is Earl episode Van Hickey, Earl and his friends start a rock band. They get drunk after the show, and attempt some debauchery with some beautiful groupies. One of the band members is a Momma's Boy, and his mom comes in with cookies. Since the woman Earl was attempting to sleep with passed out from the alcohol, Earl ended up turning to his friend's mom. ("She wasn't young, but she was conscious.") Which becomes a list item later...resulting in a Shotgun Wedding. (Or, as Earl puts it, a "pistol pressed firmly to your temple" wedding.)
The guy actually tries to get even by attempting to sleep with Earl's mom. It doesn't work.
One episode of Scrapheap Challenge had the situation where the two experts were father and son.
Host: Apparently, you've met the other expert before. Expert: (in an exaggerated whisper) Yeah, actually... I'm sleeping with his mom!
In the Penn & Teller special "Phobophilia" a guest forced to crawl through a tube filled with rats shouts to Penn "I slept with your mother! And your father!"
In The Office, Michael temporarily dates Pam's mom. She takes it really bad, giving off a Big "NO!" that lasts through an entire commercial break. They have a very tense confrontation that lasts through a few episodes, and Michael throws in her face repeatedly that he's having sex with her. So bonus points here to Michael who invoked the trope after having actually done the deed.
Dr Rudi from Australian lifestyle show parody Life Support once suggested sleeping with all one's friends' spouses, just to be able to invoke this trope and win arguments.
Hilariously subverted in That '70s Show, when Kelso and Fez mistakenly believe that Eric has banged Donna's mother and start bowing to him... in front of him and Donna. "YOU'RE A GOD!!"
In Rome, Mark Antony attempted to invoke this trope after a heated argument with Octavian as he left the room:
Octavian: I see you're still the same crude, arrogant lech you always were. (strides out)
Antony: That's right, just the same. AND STILL FUCKING YOUR MOTHER!!
Barney (with a stuffy nose): You kiss your mother with that mouth?
Ted: Like you've never said that word.
Barney: I don't kiss your mother with my mouth... yet. (Sneezes.)
Ted: Are you sick?
Barney: Is it sick to find maturity and experience sexy?
Star Trek: Deep Space Nine Gul Dukat kept Kira Meru as one of his "comfort women" during the occupation of Bajor. He gets around to telling her daughter, eventually...
Hank Moody is prone to banging a mother or two in Californication, most notably having sex with Becca's teacher which turns out to also be her current boyfriend's mom. When he surprisingly stumbles onto the boy in the kitchen after a late night romp with his mom, he mutters incredulously "I banged your mom..."
On Sleeper Cell, Christian did it with Tommy's mom. And bragged about it to his face, causing them to get into a fight. Then claimed it was a joke when Farik intervened.
In one episode of Community, Jeff and Britta plot to have him seduce the mother of a visiting teen who has been annoying them, solely so they could invoke this trope.
Old bar joke: A guy walks into a bar, sits next to a younger guy, and starts drinking. After a few too many, he turns to his seatmate and starts going, "Hey, man, I did your mom!" He does this again a few minutes later. Before he can get started the third time, the younger guy says, "Damn it, Dad, leave me alone!"
Another old bar joke: This bald guy is at an office party, and his boss comes up to him and starts rubbing his head. "Damn, Jenkins, your head is smooth as my wife's butt!" The bald guy starts to rub his head himself, and exclaims, "Well, sir, so it is!"
Crack The Case, a game in which participants ask yes/no questions to solve mysteries, featured a case in which a college student arranged for his roommate to fall to his death from a window. The motive was that he discovered the roommate was having sex with the murderer's mother.
Stand Up Comedy
This is an integral part of the comedian-heckler relationship. Jimmy Carr shows us how it's done:
Jimmy:*Holding up a T-shirt* World's Greatest Dad.note *Reverse* I fucked your mum.
Heckler: Your mum keeps calling me asking for sex.
Jimmy: My dead mum keeps calling you?
Heckler: Yeah, I'm up for it.
Jimmy: Oh, he's up for it, folks! Good for you! Well that may seem like a horrible thing for him to blurt out, but the fact is that I was warned he would be here tonight. Yeah, I was. I was warned by your mum. [...] At least, I think she was talking to me; I wasn't the only one there."
A regular response by Andrew "Dice" Clay to any vocalization (heckle or not) from his audience "Your mother... [beat], [beat], (shrug), yeah, I f***ed 'er." At least once subverted when a numerous male audience group responded from the balcony, "yeah? Your mother WE f***ed 'er!!" - Clay completely lost his "tough" in a LOL moment.
Comedian Brendon Burns can't understand why this is supposed to be an offensive insult. "My mom's 65. You're 24. Looks to me like a big result for Mom, and a big loss for you."
The RED Spy to the BLU Scout's mother in Team Fortress 2 (and based on the domination responses, the color opposites might fit as well). The BLU Spy, when discussing the Red Spy's exploits, gets perhaps the most interesting setup for the line by providing photographic evidence (see above) of the act.
BLU Scout: What're you? President of his fan club? BLU Spy: No... That would be your mother! *scatters photographs*
The Demoman also gained a domination taunt over the Medic: "Dominated! And I've been shagging your wife, ha!"
John Marston in Red Dead Redemption is often reminded, most especially by Dutch, that his wife, Abigail, used to be their gang's whore. He isn't at all fazed by that, and neither is his wife.
In Fable III, the evil gnomes will sometimes say, "I think I'm gonna come around yer house for tea... and then I'll 'ave yer mum!"
Spoofed in I Wanna Be the Guy, as it is said- in typical trope fashion as pre-bossfight taunting- by a person who actually has the right to say this without retribution, the protagonist's father.
The trope is subverted later, though, when Veronica comes to town again and starts a promising-looking sexual relationship with someone. She is somewhat nervous about breaking the news to Marten (though mostly in case he's annoyed that she'll be around more) — but Marten is just happy for her.
Ménage à 3: Zii is annoyed by an Internet troll with this as his signature. When Gary realises he knows the troll personally, Zii goes to confront him — and meets the troll's mom.note By the way, thanks to some heated debates over the morality of this action, that storyline is a taboo subject on the comic's forum. It became so controversial that even mentioning it risks ban threats.
Rex: Yeah, huh huh. We're gonna rule. Weevil: I already rule. Heh heh. I rule! Rex: You don't rule, Weevil. Weevil: I ruled your mom last night. Rex: Shut up, assmunch, that was your mom. And it was me doing the ruling. Huh huh. Weevil: Dammit, Rex!
Jaden does this in episode 16 of GX abridged.
Dimitri: You know he's struggling to fit in.
Jaden: Well I didn't struggle fitting into his momma last night.
Dimitri: E- Excuse me?
Jaden: I. Plowed. Your. Mother.
There was an old fiasco back at deviantART when the staff introduced a ridiculously flawed algorithm to sort popular deviations. Many members welcomed it, believing it will get the anime/fan art off the front page. Well the anime/fan art was instead replaced with a gif of a stick figure banging a "your mom" sign (that wasn't even made by the person who posted it).
Also, in "Chef's Salty Chocolate Balls", there is an all-new chocolatey treat called, "I Just Went and Fudged Your Mama".
Used as a Running Gag on American Dad! when Stan becomes Steve's bully to toughen him up. Done to the point that even the mother does it referring to herself.
A variation happens in Family Guy, when Quagmire's father has a sex change and then meets Brian - the only one who doesn't know. He ends up sleeping with Q's father, and later finds out the truth. So does Quagmire, who immediately goes over and kicks Brian's ass. The beat-up Brian gets up and says, "Hey, I f*** ed your dad."
Parodied in Robot Chicken with the segment "Vince Vaughn Bangs Your Mom"
It's a reference to Four Christmases where his character's mother and his ex-best friend are married.
Hank Venture does this to his best friend Dermott Fictel's mom in The Venture Bros.. Hank thought he was sleeping with Dermott's older sister Nikki but came to find out that the woman Dermott thought was his mom was his grandmother, Nikki was Dermott's mom and that the guy who knocked her up was Hank's father Rusty Venture who slept with Nikki, the president of his fan club when she was only 15. Later disgusted with the knowledge that he slept with his father's ex-girlfriend and that Dermott is his half-brother Hank has his memory wiped but leaves himself a message informing himself he wasn't a virgin.