A common soap opera scenario: young couple AliceAndBob are very happy. But [[TheVamp Vamp]] Charlene, who wants Bob herself, "casually" mentions to Alice that Bob spent the night with her (when in fact they were simply both stranded in a blizzard with thirty other people).

Given a choice between believing her beloved, who has never lied but always been faithful and true, or believing the [[HorribleJudgeOfCharacter scheming bitch]] with a [[VillainsNeverLie history of deceit]] and an obvious agenda, naturally our dumb heroine immediately accepts the worst of the story, and totally rejects her true love [[OneSideOfTheStory without even asking his side of it]]. [[BewilderingPunishment When he pathetically asks why she's upset]], she only says, "You know what you did!" with a side of DeathGlare, thus cementing what should be a DiscreditedTrope, but, sadly, is not.

At times the woman ''will'' ask the man some transparent question, such as, "Did you spend the night with Charlene?" Unfortunately, the man doesn't actually get ''why'' she's asking, and in responding with detail-free answers - or answers with the ''wrong'' details ("Why, yes - we got a lot of exercise ''that'' night. Good thing, 'cuz I was getting pretty cold.") - merely confirms the woman's fears. The woman, of course, [[PoorCommunicationKills never asks clarifying questions]] that would resolve the matter, and the man never picks up on the fact that he ''needs'' to clarify because he [[IDoNotSpeakNonverbal does not speak nonverbal]] - in fact, sometimes he'll believe that the woman knows exactly what's going on to begin with, hence the lack of necessary detail.

And of course, the woman never wonders why, if he was cheating on her, he'd just casually admit to it like that, being that he hasn't displayed {{Jerkass}} traits before. The worst part is, the accuser expects a confession, but she's only making the situation ''far'' worse.

A form of GenreBlindness, with a giant, gooey IdiotBall.



[[folder:Anime & Manga]]
* ''Manga/RanmaOneHalf''
** This is one of the problems in Akane Tendō's relationship with Ranma Saotome, of . She is willing to see the worst of anything slightly suspicious that Ranma does, something Ranma has actually [[LampshadeHanging lampshaded]] in the anime, [[CovertPervert jump to perverse conclusions]] about Ranma's goals/intentions/motivations, has been shown to [[SelectiveObliviousness consciously ignore elements of Ranma's own attempts at self-defense to prove her point and selectively remember events to further back up her opinions]] (manga version of Hinako's introduction), and believe the lies of people like Shampoo and Ukyō... who, by the way, are her devout '''rivals''' for Ranma's hand.
** Akane isn't the only person in ''Ranma ½'' who does this, though... unusually, however, the other people who do so tend to be Ranma's ''male rivals'', using this trope in relation to their particular love interest being upset and them blaming that fact on Ranma (and using it as an excuse to try and beat the hell out of him). A good example would be Ryōga and Kunō attacking Ranma after he "kissed" Akane during the first Nekoken story, an event that Ranma doesn't remember due to "Kitty Ranma" being a kind of split personality. Never mind that fact that it was Kunō who awakened "Kitty Ranma" in by exposing him to his fear of cats, but is too proud and stupid to take responsibility for the incident.
* ''Anime/FushigiBoshiNoFutagoHime'', ep 24 has bird people being teed off at the Windmill Kingdom and setting up barricades, and all one particular messenger will say is: "Why did we take such actions? King Randa (of the Windmill Kingdom) should know the reason." Naturally, King Randa is quite clueless. [=Al1701=] says in [[http://www.youtube.com/watch?v=hmb9H3GLVws#t=4m17 his review]]: "What adult would accuse another adult of doing something, then refuse to say what they did?" [[spoiler: Turns out King Randa is planning to build an amusement park in their area, or at least that's what the henchmen of the Moon Kingdom are saying. [=Al1701=] says, of the bird people simply believing them over the King, "This is a horse pill of a plot contrivance this episode's asking me to swallow."]]
* ''Manga/TokyoTribe 2'' has this with the reason why Mera wants to kill Kai. For the first several episodes, we don't know what it is, with Mera and Skunk hitting Kai with these lines early on, in flashback and in present time. As it turns out in episode 12, what Kai did was actually [[spoiler: a lie Skunk told Mera to break up his and Kai's friendship. The lie? That Kai pushed Fujio, Mera's girlfriend, in front of an incoming train. The truth? She committed suicide for unknown reasons, and Kai thought that she was accidentally pushed out of the crowd onto the tracks.]]
* The third movie of ''Anime/RebuildOfEvangelion'' [[DeconstructedTrope deconstructs]] this in a brutal fashion -- Asuka, Misato and Ritsuko are treating Shinji like crap and won't explain why, so Shinji has no idea for most of the movie that he, by complete accident, [[spoiler: ''[[ApocalypseWow nearly destroyed the world]]'']]. When he finds out what he did, [[TheAtoner he's desperate to fix it]]... but the animosity between Shinji and Asuka prevents them from finding out that [[spoiler: if Shinji tries to undo the Near Third Impact, he'll actually finish the job]].
** It goes about as badly as possible in BOTH ways. By being kept out of the loop initially Shinji doesn't find out [[spoiler: NERV is the enemy and the Rei calling him is not the one he knew and he defects as a result]]. He's later actually told but hearing the full truth only [[spoiler: causes his guilt to spiral out of control until he can't be talked out of it at all and he inadvertently follows Gendo's plan again.]]

* Used in a stand-up comedy bit by Adam Ferrara. "You know what you did," his girlfriend says. "No, seriously, what's-" "Well, if you don't know, then I'm not going to tell you!" The retort? "FINE! Then don't be surprised when this shit happens again!"
* Comes up in Drew Carey's rebuttal of the whole "[[MenUseViolenceWomenUseCommunication If women ran the world, there would be no war]]" idea.
-->'''Drew:''' [[SarcasmMode Yeah, I bet nobody would ever start a fight for no reason if women ran the world!]] "Hello, this is England. How come we're being invaded?" "Oh, I think you ''know'' why!"

[[folder:Comic Books]]
* In ''ComicBook/TheMuppetShowComicBook'', Miss Piggy believes Kermit is seeing someone else, based on a [[CrypticConversation cryptic]] and [[PhonyPsychic entirely fraudulent]] prophecy.
-->'''Piggy:''' If you don't know why I'm mad, there's no point in me telling you, is there?\\
'''Kermit:''' That doesn't make any kind of sense!
* A nonromantic variant gets played with in one issue of ''ComicBook/{{Catwoman}}''. The Trickster phones in a tip to the media that gives away her identity as mayoral candidate Selina Kyle, and she flies into a rage at him for outing her -- and then it turns out that it was meant as a generic political smear campaign and the identification was a coincidence. [[spoiler:And then he legitimately figures it out.]]
-->'''Catwoman:''' How did you ''know?!''\\
'''Trickster:''' Er... know what?\\
'''Catwoman:''' Don't play ''games'' with me!\\
'''Trickster:''' Please, God, oh please, help me figure out what she's talking about...\\
'''Catwoman:''' You... you just... made it all ''up''...?\\
'''Trickster:''' Can I get a category here? It would really help me defend myself if I knew what it was that you were going nuclear over...

[[folder:Comic Strips]]
* Parodied in [[http://www.dilbert.com/strips/comic/2006-07-04/ This]] ''ComicStrip/{{Dilbert}}'' strip: The girl ''can't'' say why she's angry, because it would violate the "Insane Chick Code of Ethics."

[[folder:Films -- Live-Action]]
* Subverted in the movie ''Film/ThirteenGoingOnThirty''. The AlphaBitch character tells Jennifer Garner's love interest played by Mark Ruffalo a nasty lie about her to get rid of him. Later we find out that while he has indeed been avoiding her, it's been for other reasons. ("It doesn't matter what Lucy said. I stopped trusting her after she stole my poprocks in the third grade.").
* Subverted nicely in the Will Smith film ''Film/{{Hitch}}'', where the object of his affections took the word of a known SmugSnake, with every reason to lie, and proceeded to break up with Hitch without explanation, then trash him in her gossip column, before confronting him at a restaurant one night. Hitch, after pausing for shock, calls her out on this and corrects her loudly in front of everyone, leaving her looking quite the fool. Then the film follows up with having her apologize and him not accept it, thus making the true climax him publicly apologizing for not accepting her apology, and begging her to come back to him.
* ''Film/WhiteChristmas''. A busybody hears part of a story that makes her think the male leads are planning to exploit their old friend. She tells everyone, including the female romantic interests, who almost leave the men over it.

* There's a old British joke playing on this trope that runs, more or less, as follows: A satirist sends every Member of Parliament an anonymous telegram reading "ALL IS KNOWN: FLY AT ONCE." The next day, half of Parliament fails to show up for work. According to legend, Creator/MarkTwain once did this [[WithFriendsLikeThese to his friends]].

[[folder:Live-Action TV]]
* ''Series/{{Monk}}'':
** In the episode "Mr. Monk and the Captain's Marriage", a police sergeant tells Captain Stottlemeyer that he's having an affair with Stottlemeyer's wife, and the captain is suspicious enough to have his wife followed, despite her protestations of innocence. And then he's ''surprised'' when she asks for a divorce. Though it also works the other way: Stottlemeyer's wife was planning to divorce him before any of that even happened, and flat-out refused to explain why when he asked. Given that the audience saw virtually nothing over the series to back her up, it made her look like quite a bitch.
** Stottlemeyer explains it himself to Monk in a later episode, the one where Monk gets shot. He's acting like a tremendous {{Jerkass}} to Natalie because he blames her for his injury, and she accepts it because she blames herself, and so due to essentially working round the clock taking care of Monk, wheeling him around in a wheelchair, etc., she is very nearly broken down. Stottlemeyer takes Monk aside, warns him that if he keeps acting like that Natalie will leave, then proceeds to state that he knows this because Monk is acting like Stottlemeyer himself and that that was why his wife left him.
* This happens to ''Series/{{Dexter}}'' during his second season. His girlfriend overhears Dexter's Narcotics Anonymous sponsor, who she's already suspicious of, mention on his answering phone that they spent the night together, and walks out on him. It's true... except it just means he fell asleep with his head in her lap after talking about his terrible childhood. She is his counselor, of sorts, after all. It's not actually shown if it was on purpose but considering how Lila turns out it would make complete sense that she did it on purpose knowing Rita would be there. However, Dexter has just recently revealed that he is a drug addict and he has been lying to her about things to hide his addiction. So it is not much of a stretch for her to believe that he would cheat on her as well. At least she does not find out that he is lying about being a drug addict and is actually a serial killer. When Rita finally confronts Dexter about it, he answers truthfully: he didn't have sex with Lila ''that'' night. Rita immediately picks up on the clarification and breaks up with Dexter. They work things out in the end, though.
* ''Series/{{Friends}}'':
** [[CloudCuckooLander Phoebe]] claims this to [[TheChewToy Ross]] in an episode. Subverted in a way in that Phoebe ''dreamed'' what Ross did, and what she dreamed was... weird.
** Inverted when Ross is supposed to have read a long tract written by Rachel about the status of their relationship, and he should have known what Rachel meant by saying "Does it or doesn't it?" Ross says, "It does," and this is what Rachel wanted to hear. But "It does" meant that Ross apologizes and admits he was wrong. This is an act of appeasement that Ross was not ready to make. And it's a problem when Rachel thinks Ross has apologized and made up, but he hasn't.
* Thomas Riker uses this to his advantage in the ''Series/StarTrekDeepSpaceNine'' episode "Defiant". Surprised by Chief O'Brien's presence aboard the titular ship, Riker cuts O'Brien's greeting off with a hard glare and "I have nothing to say to you, Chief, and I think you know why." This is because [[CloningBlues Thomas]] is impersonating William Riker at the time, and knows that a close friend like O'Brien would be able to tell the difference. So, by pretending to be mad at O'Brien over some past incident, Tom gets an excuse to avoid him, while at the same time confusing him enough that he won't press the issue.
* Subverted in ''Series/VeronicaMars'', when AlphaBitch Madison Sinclair claims that she and Logan had had sex. True to trope, Veronica believed this unquestioningly, and confronted Logan about it. They had.
* Tim and Marsha get into one of these in the penultimate episode of ''Series/{{Spaced}}''. Marsha, who believes Tim and Daisy to be a couple, has seen Tim kissing his new girlfriend and confronts him about cheating on Daisy, threatening to inform her. Tim, however, does not know this, and because Marsha does not actually explicitly say anything about what she's seen, believes that Marsha is in fact referring to a birthday cake Tim has arranged for Daisy as a nice birthday surprise. [[HilarityEnsues Complications, naturally, ensue]].
-->'''Marsha:''' If you don't tell her, then I will.\\
'''Tim:''' But you'll spoil the surprise!\\
'''Marsha:''' You ''bastard''.
* Averted in ''Series/ChinesePaladin 3''. When the heroine, who usually has some justification for her suspicions, angrily confronts the hero with this trope, he very sensibly replies "No, what did I do?" and explains what was going on. It's almost beautiful.
* Beckett confronts ''Series/{{Castle}}'' the morning after he broke the rules and saw a murder suspect that he had previously dated. [[OneDialogueTwoConversations She's talking about him messing with her chair. He's talking about kissing the suspect.]] [[spoiler:She already knew, anyway.]]
* Sketch comedy show ''Series/AlmostLive'' addresses this in a sketch about a game show called "What The Hell Have I Done Now?" wherein a confused husband tries to figure out why his wife is mad at him.
* Season 4 of ''Series/BuffyTheVampireSlayer,'' episode "The Yoko Factor". Spike goes around telling Willow, Giles and Xander in turn that the others, including Buffy, have been saying various derogatory things behind their backs. What he says or implies is different for each character, but all hit at their personal vulnerabilities and they all believe him without question. This starts a massive three-way fight until Buffy walks in and is immediately attacked on all sides, only she has no clue what the others are angry about.
* Joseph in season 6 of ''Series/HellsKitchen'' tries to simply say "They know who they are" when asked by Ramsay for his elimination nominees. When Ramsay chews him out for not giving a straight answer, Joseph gets violent and is immediately kicked off the show.
* ''Series/LostInAusten'' does this ''twice'': It turns out that Wickham's a little more honourable than Darcy says he is. [[spoiler:It turns out that Georgiana lied to Darcy, and Wickham went along with it to avoid ruining Darcy's good name.]]
* On ''Series/BetterOffTed'', Lem and Phil decide to get back at Linda by bringing her bagels and coffee every morning for two weeks and then suddenly stopping. When they tell this plan to Ted, he says, "Hey, you stopped bringing me bagels and coffee last week!" "YouKnowWhatYouDid."
* There's a refreshing and awesome subversion on ''Series/DesperateHousewives'', exactly the type of show which would (and does) play it straight. Lynette thinks that Tom is having an affair with the mother of Porter's friend; Tom knows that it's actually Porter who's having the affair, but doesn't know the identity of the "girl" in question. Lynette confronts Tom about it, he's relieved that she knows which just makes her even angrier, it all seems like it's going to lead straight into an example of this trope, ''until''... Tom, still oblivious to the fact that she's mad at ''him'', manages to get in enough words that Lynette is able to piece together the truth. [[SugarWiki/FunnyMoments Cue Porter walking in, Lynette demanding "You're having sex with your best friend's mother?!" and an epic WTF face from Tom.]]

* This [[OlderThanSteam goes as far back]] as Creator/WilliamShakespeare. In ''Theatre/{{Othello}}'', Iago's plan only succeeds because Othello decides to believe the jealous subordinate over his beloved Desdemona, and he never tells anyone what he's angry about, only that he's angry. The rest of the cast never even thinks of asking someone other than Iago about what's going on. In ''King Lear'', Gloucester decides to believe his embittered bastard son's claim that his legitimate son is a traitor, without thinking about motives or checking with anybody else.
** In ''Theatre/{{Othello}}'', it's not that simple. Iago is known by all the characters as "honest Iago" because he has a reputation for always telling the truth, being seen as incapable of doing anything other than tell it like it is. Add in that Iago and Othello have fought in battles many times before to the extent that Othello has built up an absolute trust in Iago, who was always with him in the heat of battle. Though Othello does not ask Desdemona about this, Iago has a hand in this, saying first that Desdemona would just deny it and then that Desdemona deceived her father to marry Othello, when Othello questions why Desdemona would betray him when she has such a loyal character.
** Also done in the play ''MuchAdoAboutNothing'', but with the genders switched round. Hero and Claudio are to be married the next morning- but the evil Don John convinces the court that Hero has been sleeping around. The entire court (except for the heroes) [[IdiotBall immediately believe]] the deceitful Prince that previously tried to overthrow the court. Of course, in fairness, they ''thought'' they'd actually seen Hero in the act...

[[folder:Web Comics]]
* Subverted in a subplot of the webcomic ''Webcomic/DominicDeegan''. ManipulativeBastard Neilen Everstar tries to convince the protagonist and his girlfriend, respectively, that the other is discontent with the state of their otherwise happy relationship. Dominic being a seer invalidates the first half, but given Luna's propensity toward self-loathing, one would almost expect his ploy with her to be preordained to succeed. However, [[AwLookTheyReallyDoLoveEachOther this isn't the case.]] While Dominic being a seer makes it impossible to fool him, the reason he doesn't warn Luna is because he trusts her enough to believe she would see through the trick. He was right.
* A purely accidental version occurs in ''Webcomic/SequentialArt'', where Kat slumps face-first into Art's crotch while the two are sleeping on the couch, and accuses Art of being a pervert when she wakes up to find herself in said compromising position, leaving Art confused by her outburst since he was asleep when it happened. However, she learns this little detail from Pip soon after and apologizes to a still-confused Art.

[[folder:Western Animation]]
* ''WesternAnimation/CodenameKidsNextDoor'' "Operation Dogfight" doesn't actually use the phrase, but it's a YKWYD plot anyway, and one that works to boot: some kid who has shot down Numbuh 2 several times walks in with a chili dog into a hobby shop where 2 is shopping and gives 2 a DeathGlare. At first go, one is led to conclude that he's being all "Hey, I'M the new king of the sky now, so stay out!" [[spoiler:However, when they both shoot each other down, the kid is all "At least I stopped you from bombing the chili dog factory," and it becomes obvious that the kid was actually giving him a "You know what you're doing" glare from having heard from the shop owner that 2 was planning to do just that. With both of their planes wrecked and out of the way, the shop owner goes off to bomb the chili dog factory himself, [[DisproportionateRetribution angry at how customers always spill chili sauce on his counter]].]]
* Said in one episode of ''WesternAnimation/FostersHomeForImaginaryFriends'' but quickly subverted as the character who said it was joking around.
* An episode of ''WesternAnimation/JimmyTwoShoes'' had Beezy being haunted by a [[OurGhostsAreDifferent ghost]]. When he tries to figure out why, the ghost simply replies "You know what you did."
* In an episode of ''WesternAnimation/{{Doug}}'', the title character manages to destroy a condemned house [[WithThisHerring with a single rock]] to impress [[ObliviousToLove Patti]]. However, this causes her to hate him for the duration of the episode because [[spoiler: it was ''her'' old house back when her mother was still alive.]] The episode is exacerbated because Patti (and later Bebe, who asks her about it on Doug's request) refuse to pass that information onto Doug. His best friend Skeeter thought he knew about it, since ''everyone'' in town knows it, forgetting that he just recently moved to town. At the end, Patti apologized for being angry at him.
* Parodied in ''WesternAnimation/DrawnTogether''. A housemate will make a disparaging remark about Tori Spelling, to which another housemate will ask "why you dissing on Tori?" The response is "she knows what she did" followed by dramatic background music.
* In that cartoon where an attempt to turn The Thing of the ''WesternAnimation/FantasticFour'' back into human turned him into a ''teenage'' boy, he attended school and there was one episode where the bullies framed him and, when he asked the teacher why she'd want to talk to him, she said something among the lines of "As if you don't know."
* An episode of ''WesternAnimation/{{Horseland}}'' had one of the girls incorrectly blamed for spreading gossip when she was overheard talking about a celebrity with the same name as one of her friends. The rest of her friends began to snub her while she herself had no idea what was going on until episode's end. Once she knows the situation, she immediately clears everything up.
* ''WesternAnimation/ThePowerpuffGirls'':
** Blossom in the episode "A Very Special Blossom." She steals a set of golf clubs to give the Professor for Father's Day. When the heat's on (read: the Professor, seen with the clubs, is arrested for theft), she ambushes Mojo Jojo, trusses him up and tries to frame him for the theft. Buttercup and Bubbles don't believe her for a second, and a beatdown among the three takes place until Blossom confesses.
** In "Curses", the girls unwittingly pick up swearing after they overheard the Professor doing it. When they curse in school, Miss Keane [[SoapPunishment washes their mouths out]]. When they asked what they did to deserve it, she tells them "You know perfectly well what you did."
* The infamous episode of ''WesternAnimation/TheFlintstones'' where Fred unknowingly switches places with [[IdenticalStranger an identical tycoon]] who acts like a jerk to Wilma, Betty and Barney, and when Fred gets home Barney beats him up and Fred has no idea what prompted it.
* ''WesternAnimation/MyLittlePonyFriendshipIsMagic''
** In "For Whom the Sweetie Belle Tolls", Sweetie Belle accuses Rarity of deliberately upstaging her just like she did at her fifth birthday party, but Rarity doesn't know what she's talking about. Later in her dreams, Princess Luna flashes Sweetie Belle back to the party in question and shows her the truth behind what happened that day.
** In the episode "The Hooffields and [=McColts=]", Twilight and Fluttershy are roped into trying to end a feud between two families. When trying to find out how the feud started, both family leaders respond with "They know what they did." [[LampshadeHanging Twilight sees this as a sign that neither of them knows what the other did.]]

[[folder:Real Life]]
* When Activision fired two Infinity Ward employees for insubordination, they said something to this effect.
* Pretty much everyone alive has a story of being confronted by a friend or loved one only to be given this stock line when asking what they did wrong. Similarly, children are also subjected to this trope by their parents or teachers when they do something wrong, even if they honestly don't know what they had done wrong.
* {{Defied}} by the Sixth Amendment of the United States Constitution for the reason that some nations did this ([[TruthInTelevision and some still do]]):
-->In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and '''to be informed of the nature and cause of the accusation''';...
* When contracting in the United States, if the company lets you go or doesn't extend your contract (as opposed to firing you), it's not uncommon for them to not explain why. This is logical, since it invariably deals with company information, and you're not part of the company anymore, but this doesn't make it any less frustrating.
* According to Creator/YoshiyukiTomino, this is one of the reasons for removing an episode of ''Anime/MobileSuitGundam'' towards its director. He's never said what that reason was, though.
* If someone is disinherited in a will, it will generally be for "reasons you are aware of" or similar language. Because the person who wrote it is [[CaptainObvious not around to defend their decision]], a specific reason could be contested in court, whereas vague language cannot.
* This basically happened in the correspondence which led to the fatal duel between Alexander Hamilton and Aaron Burr. Someone had apparently told Burr that Hamilton offered "a still more despicable opinion" of him. Burr demanded that Hamilton either deny it or apologize, Hamilton responded that he couldn't do either if he didn't know what he was accused of saying. Burr wanted an apology anyway. (It's quite likely that he was deliberately trying to pick a fight).