[[quoteright:350:[[Film/{{Superbad}} http://static.tvtropes.org/pmwiki/pub/images/mclovin_fake_id_hawaii_11.jpg]]]]
[[caption-width-right:350:"Alright, you look like a future pedophile in this picture, No. 1. No. 2: It doesn't even have a first name, it just says [=McLovin=]!"]]
->'''Homer''': Hello, [[PaperThinDisguise my name is Mr. Burns]]. I believe you have a letter for me.
->'''Postal Worker''': Okay. What's your first name, Mr. Burns?
->'''Homer''': ''[{{beat}}]'' ...I don't know!
-->-- ''WesternAnimation/TheSimpsons''

This trope is when a character, in disguise or otherwise pretending to be someone else, doesn't know some basic piece of information about the person they're pretending to be. This could be because they didn't research the identity enough, or maybe the disguise and cover identity were done in a rush and they didn't think all the way through.

A quick-thinking character might be able to bluff their way out of the situation, either through a LineOfSightName, using their RealNameAsAnAlias, or simply pulling the BavarianFireDrill. This can backfire if they [[OutOfCharacterAlert say the wrong thing]], mess up the TrustPassword, or if the person they're trying to fool is [[BluffTheImpostor already suspicious]]. Otherwise, HilarityEnsues as the character either tries to play it straight (i.e., they've [[TooDumbToLive somehow ''forgotten'']] their first name, birthdate, hometown, etc...) or just tries to [[TheExitIsThatWay awkwardly escape]]. In drama, this might lead to a tense situation where the character is found out and has to escape without being caught.

Compare StereoFibbing, for when two characters have to make up a lie on the spot to get out of this situation.
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!!Examples:
[[AC: AnimeAndManga]]
* Similar to RealLife example below about checking age, ''Manga/KamenNoMaidGuy'' has an example where the twenty-something NinjaMaid Tsurara tried to infiltrate Naeka's school as a student. The usually ditzy Naeka asked her which EasternZodiac year is her birthday in. For people in heavily Chinese-influenced country, your own zodiac year is something you already know and and can be answered without thinking. Calculating your supposed birth year from a fake age and come up with zodiac year for it, though, would take several seconds and some finger-counting.
* In ''Anime/LupinIIIDeadOrAlive'', Olčander is able to see through Lupin's disguise because [[spoiler: of how it felt to kiss Pannish]]. In the Dub, Lupin jokes he needs more practice. In the Sub, [[spoiler: it is because Pannish never smoked]]. She doesn't seem upset about the disguise, and continues to work with him afterwards.

[[AC:AnimatedFilms]]
* Subverted in ''WesternAnimation/ToyStory3''. Barbie uses an astronaut suit to disguise herself as Ken to talk with the Bookworm. The suit covers her head and face, and almost her whole body...except her feet, and she forgot to change her high heels, which the Bookworm sees as she walks away. Fortunately, the Bookworm dismisses the high heels as one of [[TheDandy Ken's idiosyncrasies]].
* The title character of ''Disney/{{Mulan}}'' does this when asked her name. Her family name (which she must use as part of the cover story) is Fa, but she hasn't thought of a ''personal'' name, leading to a very awkward conversation where Mushu tries to secretly help her come up with a name.
** One of his suggestions is [[PunnyName Ah Chu]].
*** Which would have lead to the cover identity being ''Fa Ah Chu''.
*** Like ''Fa Ping'' is any better?
* In ''Disney/WreckItRalph'', Ralph tries to pose as a candy cane tree inspector while quizzed by Vanellope, but she sees through this lie immediately because he clearly knows nothing about her game world.

[[AC:ComicBooks]]
* In the early 1990s ''SpiderMan'' arc where Peter Parker's parents returned from the dead, May realized they were imposters when they refer to the wrong date for their anniversary, indicating that they somehow didn't know about their secret wedding several months prior.

[[AC:{{Film}}]]
* Played with in the movie ''SuperBad'', where one of the teenage kids gets a terrible fake ID that only has the name "[=McLovin=]".
** It actually appears to fool the cops, and they end up going on an adventure with the kid. Subverted in the end, when they reveal that they immediately saw through the fake but wanted to have some fun.
* In ''RomyAndMichelesHighSchoolReunion'' they are pretending to be "successful businesswomen" to impress people. It is only when a waitress asks them what business they are in that they realise they may have neglected a vital element of their cover story.
** During a dream sequence, Michele actually supports her cover by rattling off a complex but plausible method of developing the adhesive. Interestingly enough, it wasn't scripted - the actress improvised thanks to actually having an education in science.
* In ''Film/StarWarsANewHope'', Han and Luke are disguised as stormtroopers aboard the Death Star, to rescue Princess Leia, when they're forced into a shootout with some real stormtroopers. After killing them, Han rushes to a com unit to try and fool the troopers on the other line that nothing's wrong, and the following conversation takes place:
-->'''Han''': ''[sounding official]'' Uh, everything's under control. Situation normal. \\
''Voice'': What happened? \\
'''Han''': Uh, we had a slight weapons malfunction, but uh... everything's perfectly all right now. We're fine. We're all fine here now, thank you. How are you? \\
''Voice'': We're sending a squad up. \\
'''Han''': Uh, uh... negative, negative. [[BlatantLies We had a reactor leak here now]]. Give us a few minutes to lock it down. Large leak, very dangerous. \\
''Voice'': Who is this? What's your operating number? \\
'''Han''': Uh... \\
''[Han shoots the intercom]'' \\
'''Han''': ''[muttering]'' Boring conversation, anyway. LUKE! WE'RE GONNA HAVE COMPANY!
* In the final sequence of ''Film/{{Stalag 17}}'', Sefton confronts [[spoiler:Price]], the [[TheMole Nazi double agent]] in the [=PoW=] barracks, and asks him if he remembers what he was doing when he heard that Pearl Harbor had been attacked. [[spoiler:Price]], who claims to be a Cleveland native, says that he was having dinner... but since the attack took place in the early morning in Hawaii, it would have been lunchtime in Cleveland, whereas it would have been evening in Germany.
* StarTrekTheNextGeneration: In 'Future Imperfect', a boy posing as Riker's son misses a vital piece of information about the woman he claims is his mother - [[spoiler: she only ever existed as a hologram]].

[[AC:{{Literature}}]]
* ''Literature/SkulduggeryPleasant''. Scapegrace has a problem that causes him to invent a twin brother, of course he gets every detail right and thinks of everything....except one of the names.
* ''Literature/HarryPotter''
** In ''Literature/HarryPotterAndTheChamberOfSecrets'', Harry & Ron use Polyjuice Potion to pretend to be Crabbe & Goyle, but their infiltration of Slytherin House is stymied by the fact that they don't know how to get in to Slytherin's chambers. They ask a passing student, but she's from Ravenclaw. Fortunately, Crabbe and Goyle are so dim that they're not really acting out of character. They asked the Ravenclaw where the common room was, and were lead there by Draco. They had an OhCrap moment when Draco asked them the password, but were saved when Draco remembered it before they did. Other instances of them being out of character for Crabbe and Goyle are when Harry didn't know what Azkaban was and when both of them forgot to laugh at a ''Daily Prophet'' article where Ron's dad gets in trouble with the Ministry.\\\
In the movie, Harry almost gives it away by still wearing his glasses. He quickly excuses them as reading glasses, causing Malfoy to stare at him skeptically and, [[ThrowItIn courtesy of an adlib by Tom Felton]], to remark that he didn't know "Goyle" knew how to read.
** [[ChekhovsGun The specific example of the location of the Slytherin common room comes up again]] in ''Literature/HarryPotterAndTheDeathlyHallows'', when Scabior says people have claimed to be Slytherins when caught by his gang of Snatchers but couldn't say where the common room is. Because of his previous experience, Harry can actually answer this question which throws Scabior for a moment, but not enough to let Harry go.
* Literature/AlexRider very nearly gets himself killed because of these.
* [[XWingSeries Face Loran]], in disguise as [[SmallNameBigEgo Captain Darillian]], stumbles into one of these when Admiral Trigit uses an Imperial Intelligence code phrase which he doesn't recognize but Darillian should know instinctively. The Alliance agents do come up with the explanation of the code phrase for him (after a few seconds), but Trigit is still suspicious. [[MagnificentBastard Naturally]], Face bluffs his way out of it, first by [[SarcasticConfession seemingly confessing the truth]] ([[ThatManIsDead "I'm not the Zurel Darillian you knew"]]), then by distracting Trigit with [[RefugeInAudacity a tale of having been in love with Ysanne Isard]].
** Or, more specifically, of having an unrequited crush on Ysanne Isard, bringing out a TON of background info to overwhelm Trigit, AND finally bringing up a detail only someone who met Ysanne Isard would know. Namely, the specific perfume she wears, which Face knew because he met her once, and only once. The ship applauds.
* ''ASongOfIceAndFire''. While on her quest to find the fugitive Sansa Stark, [[ActionGirl Brienne]] of Tarth claims she's looking for her sister, but forgets to think up a false name for her. It's a moot point anyway, as most people can tell who she's looking for just from the description, given that she's rather high-profile (when [[spoiler:the heir to the North]] is a suspect in [[spoiler:the murder of the King]], word gets around) and there's [[BountyHunter a lot of other people searching for her]].
* ''On Wings of Eagles'' by Ken Follett. 'Bull' Simons insists that the EDS men he's taking out of Iran learn the details on their fake passports off by heart. Everyone thinks this is an unnecessary precaution until just before they reach the border, when they're stopped at a guerilla checkpoint and grilled on these exact details.
* Several of these in ''The Spycatcher's Omnibus'' by Lt. Colonel Oreste Pinto. In one case, Pinto is alarmed to discover a high-ranking British official who is a notorious ladies man has got himself a new SexySecretary, a refugee from German-occupied France who did not pass through the routine security clearance. He has to do an ad-hoc interrogation there and then, with the official constantly demanding Pinto hurry up (despite the fact that such interrogations normally take days). Pinto suddenly has the idea of telling the woman to take off her shoes, which reveals her nice soft feet -- despite her claiming to have walked all the way from France over the mountains to Spain. The official is flabbergasted when Pinto informs him his secretary has just confessed to being a German agent.
* The Literature/TommyAndTuppence novel ''N or M?''
** Tuppence is undercover as an "unofficial" agent at a seaside inn attempting to root out a German spy. She has made up her own elaborate back story where she has three sons, one serving in each branch of the military, who send her letters in secret code. At one point, she talks about her "own two", momentarily confusing her real-life twins with the made-up sons. When called on it by the inn's owner, she covers it by explaining that two of her sons were very close in age and spent more time together than with the third sibling.
** Tommy, undercover at the same time, averts this; his background was made up by the intelligence agency he's working for to fit in neatly with his existing life and not be too elaborate to remember.

[[AC:LiveActionTV]]
* The British comedy series ''{{Spaced}}'' features Tim and Daisy, who are pretending to be a couple in order to rent an apartment. Though they attempt to be as thorough as possible by learning a multitude of mundane details about each other ("I forgot what you got for your fifth birthday!" "Miniature drum kit"), they get caught in their lie while fumbling around regarding what day they had sex first vs. what day they kissed first.
** A much worse mistake is barely averted as, just before they go in, they realize they've never learned each other's names.
* Subverted in the ''Series/{{Farscape}}'' episode "Losing Time." The crew are informed that an "energy rider" had invaded the body of one of them and that they can find out who it is since the rider won't know "details of the heart" like family members. They get misdirected when a new member of the crew tells a different story about her background than the one she initially told them and they assume she's lying. In truth she'd been lying the first time.
* Came up in ''Series/BurnNotice'' as early as the second episode. Mike is impersonating a friend of a friend of the Villain of the Week, Quentin King. Quentin slips a BluffTheImpostor into an offhand remark about their mutual cellmate Paco. The Department of Corrections file Mike used as a source for his cover ID didn't say whether Paco drank, so Mike guesses that he didn't. He was right[[note]]He points out later that he had a 50/50 chance of being right, and correctly guessed that it was a BluffTheImpostor question. He then points out in the narration that this happens to spies ''all the time''[[/note]].
** In later episodes, he gives examples of what to do if the Cover Identity Anomaly slips during a BluffTheImpostor moment: ''keep lying''[[labelnote:*]]"Some spies, when their cover looks like it's going to be blown, will drop the pretense and retreat. ''Good'' spies will ''lie harder''."[[/labelnote]]. In a similar case to the above, he's asked a question and gives the wrong answer (it's another drinking question, and he says that the friend of a friend never drank). When the target calls him on it, Mike simply says that the friend of a friend gave up drinking in prison and found religion, which the target thinks about and accepts.
* ''Series/GameOfThrones''. Brienne is escorting Jaime Lannister back to King's Landing when three Northern soldiers recognise him as the notorious Kingslayer. Naturally they deny it, with Brienne claiming Jaime is a thief she is taking to Riverrun to be thrown in the dungeons.
-->'''Soldier:''' I've a question for you both, and I want you [[StereoFibbing both to answer it at the same time]]. I count to three, you both answer. What's his name? One...two...three...
-->''(Brienne and Jaime exchange a MeaningfulLook, then she [[BadAss kills all three soldiers.]])''
* This almost gets Callan killed in an episode of ''Series/NCISLosAngeles''. The team intercepts the communications of a terrorist cell and realize that the terrorists are expecting a new member to arrive whom they have apparently never met before. They arrest the terrorist and Callen takes his place. However, the cell's leader actually went to school with the man Callen is impersonating. They were very young at the time and never became friends so Callan is able to bluff his way through the questions he is asked. However, he trips himself up because in their hurry to make the switch, the team failed to realize that the new terrorist is left-handed. The cell leader clearly remembered this about his former schoolmate and when he sees Callen write using his right hand, he knows that they are being tricked.
* In the ''Series/BeingHuman'' episode "The War Child", Eve is being smuggled into a [[PuttingOnTheReich concentration camp]] by a freedom fighter claiming to be her father. Unfortunately, Mr. Snow tests this story by asking the man what colour Eve's eyes are. He doesn't know.
* This is narrowly averted in the pilot of ''Series/{{Graceland}}''. Mike has to go undercover as the brother-in-law of a low level drug dealer in order to prevent Russian mobsters from killing the dealer's family. The brother-in-law is a real person with a criminal record that the Russians are aware of. Mike only vaguely matches the man's description and is shorter and thinner than him. They compensate by having him wear platform shoes and blaming the weight loss on drug use. Mike still almost gets caught when he has to tell the Russians about a murder he claims to have committed and the FBI agents listening in on the conversation from MissionControl have to quickly create a fake crime report that matches what Mike said and insert it into the relevant police databases.
** In another episode Mike pre-empts this when he pretends to be Marine selling stolen military weapons. Almost immediately after selling the weapons to a gang, the gang gets hijacked by another gang which takes those weapons. When the angry gang leader suspects a setup and questions Mike about his whereabouts during this hijack, Mike angrily tells them that he was on base and they can easily verify it by checking with his duty sergeant. The sergeant does not exist but Mike knows that, unlike the Russian mobsters, these gang bangers do not have the contacts to verify his story or even confirm that someone with that name is even enlisted in the Marine Corps.
* In ''Series/PersonOfInterest'' an executive at a computer security company tries to send flowers to the parents of an employee killed in a traffic accident. When it turns out that the parents do not exist, she quickly realizes that the man was a Chinese spy. She also realizes that someone high up in the company must have been working with the spy or this would have come up on a routine background check. It turns out that [[spoiler: many of the company's employees, including most of the executives, were Chinese spies]].
** The Machine has Root and Shaw infiltrate a CIA black site by having them pretend that Shaw is a CIA agent delivering Root as a prisoner. The Machine is unable to obtain all the correct security codes so Shaw has to say that she was in a hurry and forgot to get the new codes. The suspicious guard is about to radio in to his superiors for verification of her identity but his radio malfunctions. Shaw is able to tell him the correct procedure for resetting the radio. The procedure was designed specifically to prevent unauthorized personnel from using the black site's equipment so the guard accepts this as proof that Shaw really is part of the unit.
* One episode of ''DegrassiJuniorHigh'' has Snake trying to get alcohol for a party. It would all be well and good except for the fact that the fake ID doesn't even have a picture on it.
* ''Series/DeathInParadise'': In "Death of a Detective", a woman has assumed the identity of her sister. However, she had never read the novel on which her sister did her dissertation at Cambridge.
* On ''Series/{{Turn}}'' an American agent is trying to infiltrate British-occupied New York by posing as British officer who was captured by the Americans and is being exchanged in a prisoner swap. The agent is quickly discovered when he does not know his regiment's motto and later makes a few more mistakes including failing basic European dinner etiquette by holding his fork in his left hand.
* An episode of ''Series/VeronicaMars'' deals with Veronica's dad, who has been temporarily reinstated as sheriff, cracking down on bars that serve alcohol to minors despite the obviously fake [=IDs=]. The only two teens whose [=IDs=] are ''very'' good Sheriff Mars happens to know personally, and he also happens to know that they were laminated using his own ID card printer. He then has his deputies conduct random ID checks at bars. When that doesn't yield results, he sets up the same two teens with obvious fakes (with pictures of [[Music/BonJovi Jon Bon Jovi]] and [[Music/TheNotoriousBIG Biggie Smalls]]) and has them drinking non-alcoholic beer at a bar about to be inspected by one of his deputies. When the deputy doesn't attempt to arrest the two teens despite the obvious fakes, the sheriff has him and three others fired.
* ''Series/TheSaint'': In "The Organisation Man", Templar, working undercover for British military intelligence, has infiltrated a small [[PrivateMilitaryContractor private army]] whose current assignment is to [[spoiler:liberate a captured, high-profile spy]]. They're disguised in the stolen tartans of a detachment of Scottish soldiers who were due to take over guard duty, and on handover, are being inspected by the current guard commander. Their disguises are perfect (as befits a regiment known for their punctilious attention to detail), up until [[OhCrap the point]] when the commander notices that [[spoiler: they've all placed their [[NationalWeapon sgian-dubh]] knives in the wrong sock - the right rather than the left]].

[[AC:Radio]]
* [[MysteryWriterDetective Paul Temple]] and his wife Steve, in addition to revealing impostors by using [[BluffTheImpostor a question or comment]], have a couple of occasions where an impostor simply gets one detail wrong.
** In ''Paul Temple and the Alex Affair'', Temple gets a phone call from his friend Leo Brent, whom he has sent to stake out a hotel. The caller is a plausible impostor, but his error is [[spoiler:addressing Temple several times as 'Paul', when, as Temple remarks to Steve, Brent ''always'' calls him 'Temple'.]]
** In one episode, Steve receives a phone call from another very plausible impostor claiming to be her husband. The only way she knows it isn't him is [[spoiler:because he uses the expression "By George!" rather than his usual "By Timothy!"]]

[[AC:RealLife]]
* This is the point of "Security Questions" on websites when you need to reset your password; they're intended to foil someone pretending to be you, by asking questions that only you should know the answer to.
** Some places invert this and actually advise you to put something that is completely wrong (but that nobody would guess) as the answer, for example if the question is "What is your birthday?" put "Puppy", so that if the pretender does find out your info they can't get into your accounts. (This assumes, of course, that the system will accept such an answer to ''that'' particular question; for a system that accepts only ''dates'' for a "birthday" question, one can still enter a wrong date.)
* Standard tradecraft for spies when communicating is, to give a hint to their controllers if someone was faking their communications, to have a subtle challenge code that, assuming the spy hadn't gone full DoubleAgent, would be something the faker wouldn't be able to respond correctly to or even realize they were expected to respond to. The same principle was used for dead-drops: often a legitimate drop required some subtle thing at ''another'' location to verify the drop.
* One quick check used in stores to challenge customers who appear too young for the purchase (typically alcohol and/or cigarettes) and might have a fake ID is to ask what year they were born. Someone faking their age is likely to trip up and give their actual birth year or obviously have to stop and think about what year they would have had to have been born to be legal.
** A similar practice works (less reliably) for signature forgers. While the person is signing their name, if they're asked a question that they have to stop and think about, they're more likely to mess up their signature if they're not used to writing it.

[[AC:TabletopGames]]
* This is a suggested possibility for ''TabletopGame/{{Shadowrun}}'' characters whose false identities fail security scans. On a critical glitch, a suggestion is that some part of the data is clearly false (e.g. an elf's SIN identifies him as a female troll).

[[AC:VideoGames]]
* One mission in ''VideoGame/MechAssault'' has the player pilot a captured enemy Thor into a Word of Blake base to download some intel from their computers. The disguise almost works, until one of the Blake officers asks you to transmit your ID code or be fired upon. Fortunately, they wait just long enough for Foster to download the intel.
* In ''VisualNovel/PhoenixWrightAceAttorney: Trials and Tribulations'', an impersonator doesn't know that the person he's imitating recently suffered an injury that made him [[spoiler: unable to hear out of his left ear]]. When a witness who was fooled by the imitation testifies that the person was [[spoiler: wearing an earpiece in his left ear]], Phoenix has to point out that it makes no sense.
* In ''TalesOfSymphoniaDawnOfTheNewWorld'': [[spoiler: Emil Castagnier]]. [[spoiler: Being the summon spirit Ratatosk in human form, Emil]] lacks a lot of information that would be expected from a resident of [[spoiler:Palmacosta - fishing, the Desian Human Ranch nearby, etc.]] Subverted in that [[spoiler: he is unaware of what he is BeneathTheMask for most of the game]]
* In a mission in ''VideoGame/{{Hitman}} 2: Silent Assassin'', Agent 47 can adopt a disguise of a "Lord Sinclair" to get close to his target (a female doctor). If she asks 47 for the name of "his" wife, though, he won't know what to say before eventually randomly coming up with "Elsie" (which is way off the mark), blowing his cover.
* In ''VideoGame/SaintsRowTheThird'', the Boss disguises himself as Cyrus Temple, the leader of S.T.A.G., to infiltrate their base and save Shaundi. While MagicPlasticSurgery means the looks and voice are perfect, the Boss makes little to no attempt to try and ''speak'' like Cyrus. Depending on your chosen voice and gender, this can result in "Cyrus" doing things like hitting on his subordinate, talking about how cute a guy is, or speaking in various accents.

[[AC:WesternAnimation]]
* ''WesternAnimation/TheSimpsons'':
** The page-quote above, where Homer attempts to pretend he's Mr. Burns... except he doesn't know what Mr. Burns's first name is.
*** For added laughs, this was early enough in the show that it's possible Mr. Burns hadn't even been given a first name yet (it definitely had not been mentioned in the show).
** When Homer pretended to be the pianist from the movie ''{{Shine}}''. When asked for his name, he responds "[[IAmNotShazam Shiny McShine]]".
* ''WesternAnimation/AvatarTheLastAirbender'' has Sokka trying to pass himself and his sister Katara off as Aang's parents when he gets in trouble with his teacher at a Fire Nation school[[note]] Trust us, ItMakesSenseInContext, it really does[[/note]], leading to the hilariously BadAss PaperThinDisguise identify of Fire. ''[[InherentlyFunnyWords WANG]]'' [[AwesomeMcCoolName Fire!]]. And his wife, Sapphire Fire. As with many examples of RefugeInAudacity on the show, this works beyond any reasonable expectation [[RuleOfFunny because it's funny.]]
* In the ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' episode "Spike At Your Service" the main characters stage a fake Timberwolf attack for Spike to rescue Applejack from, and Spike is fooled at first, until he notices that the fake Timberwolf doesn't have bad breath.
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