Yesterday, Alice was pranked by Bob, who came to work dressed as Superdude. Today, the real Superdude shows up unannounced. Alice sees Superdude and assumes it's Bob again. She says, "Ha, Ha, nice try Bob!" and tries to pull off his mask.
Basically whenever a celebrity, superhero, villain, alien, monster, etc. appears, but other characters who see it are not unusually excited, surprised, or frightened, because they automatically assume it's a hoax, on the basis that another character tried to do something like that earlier.
- When Played for Drama, it can become Not a Mask. However, in modern usage, it's predominantly a comedy trope, as seen below.
- When it's Played for Laughs, this can become For Halloween, I Am Going as Myself or, more often, Your Costume Needs Work.
- When the characters originally believed that the "impostor" was part of a deliberately staged situation, it overlaps with And You Thought It Was a Game.
- Often a karmic punishment for someone who runs a Monster Protection Racket or was Crying Wolf.
- The inversion of Mistaken for an Impostor, where a seemingly powerful being is actually a relatively harmless con artist or hoaxster in disguise, is a "Scooby-Doo" Hoax.
- If the audience knows that the real monster really was there, but the characters never find out, that's Not-So-Imaginary Friend or the masquerade.
- If they find out but only after it left and so they are unable to confirm it, it is Real After All.
- If it's merely played with by having neither the audience nor the characters really know what really happened, see Maybe Magic, Maybe Mundane.
- It can be used as a misdirection technique by The Men in Black, The Chessmaster, the Devil in Plain Sight or a Clark Kenting hero.
- It can also be used with an Identical Stranger plot, where the real star looks exactly like the prankster.
- In one ad for The Late Show with Stephen Colbert, Colbert lists the types of people he will be interviewing on his show, while walking past actors made to look like those examples. When finally reaching "politicians", Colbert walks up to who he assumes is an actor portraying Mitt Romney. Turns out that he really is Mitt Romney (he was promised pancakes for his appearance), but Colbert continues to assume that he's just a really good actor.
Mitt Romney: I am Mitt Romney.
Stephen Colbert: That's it! Stay in character.
- In Sailor Moon, the Three Lights are doing a movie that has a monster in it that looks a lot like the actual monster that the Senshi end up having to fight. At first Seiya disguises himself as the monster, meanwhile the actual monster scares the Senshi first. Taiki and Yaten at first play along and run away doing fake screams commenting that Seiya's getting into it too much. Taiki notes that Seiya had a chainsaw (part of the movie monster costume) but the real monster doesn't have one. Then Seiya comes along and they tell him that's enough scaring people, but Seiya is confused because he hasn't done anything yet and he asks where Usagi and her friends are. Then Taiki and Yaten realize that the monster was real and run off, leaving Seiya all confused.
- An InuYasha episode had a variant of this, the youkai had been dealing with several of Shippo's gimmicks and illusions, and when Inuyasha walked out of the tall grass, he thought it was another trick. It wasn't, as the youkai found out the hard way.
- In an episode of the 2003 anime version of Fullmetal Alchemist, the Elric brothers are shunned in one town they visit...for claiming to be the Elric brothers. It is implied that at least one townsperson knew the other set was fake, but went along with the ruse out of sympathy for the poor orphans.
- Hayate the Combat Butler dealt with this (~Ch 255). The characters decided to have a costume party, and then a bunch of real monsters got summoned in their midst. Some of the characters were truly scared (and protected by the stronger characters), others recruited the monsters' services for their own tasks. Not all the characters seem to have caught on they were dealing with actual monsters.
- Bone: Phoney Bone runs a dragon protection racket so that he could run off with all the town's valuables. The hoax becomes far more complicated when a real dragon, who happens to be a good friend of his cousin, intentionally gets caught in his fake snare just to see what he would do.
- In this Donald Duck comic, "Lost Valley", Donald, who through a series of unfortunate events was roped into becoming a tour guide in the Amazon, comes upon an evil intelligent ape and thinks it's Daisy, who was dressed up earlier as one of them to infiltrate their temple. He then tries to help "Daisy" out of her "costume".
- Calvin is derailed by this while using his Stupendous Man costume to mess with his class and disrupt one of his tests. Nobody believes Stupendous Man is anyone other than Calvin in a hood and cape.
- In one early story, Spider-Man was too ill to fight effectively and was easily beaten and unmasked by Doc Ock. His poor performance made everyone think that he was just Peter Parker pulling a really stupid stunt.
- In "The Short Halloween", a drunken man in a Spider-Man costume leaves his friends to throw up in an alley and passes out at exactly the same time as the real Spidey is rendered unconscious by a lucky shot from a one-shot villain and falls into the same alley. The drunk's friends drag the real Spidey back to their apartment, while the villain's team capture the drunk. Hilarity Ensues.
- The Silver Age story "The Batman Nobody Knows" features Bruce Wayne camping with some scouts, and listening to them regale each other with their theories about who/what Batman really is. These stories range from plausible-but-inaccurate to the supernatural. Finally, Bruce leaps from the bushes in his Batsuit to surprise the campers. Much to Batman's amusement, the kids don't buy it.
- There's an Archie Comics story in which Veronica has Archie masquerade as her dad at the school's father-daughter dance, since Mr. Lodge had to go on a business trip. She gets angry with Archie at some point and then he goes outside, where he finds Mr. Lodge, who cancelled said business trip so he could go to the dance. Mr. Lodge arrives at the dance, but Veronica, still angry with Archie, attempts to expose him and finds out the hard way that she's yelling at her father.
- In the UK G1 Transformers comic, when Optimus Prime returns to Cybertron, a disinformation campaign by the Decepticons leads to Ultra Magnus and the other Autobots believing him to be a Decepticon spy disguised as Optimus Prime and coming very close to executing him.
- In H'el on Earth, Lois Lane mistook Supergirl for a "comely cosplayer" at their first meeting, mostly because she walked into Clark Kent's apartment when Clark and Lois were arguing with each other and romantic jealousy had cropped up.
- In Superman: Truth, both Lex Luthor and new Batman former Commissioner Gordon believe that Clark Kent is just parading around in a Superman shirt claiming to be the real deal and that the real one is missing and hadn't had his identity exposed. This is only because Supes is significantly weaker, thus can't pull off his usual stunts.
- Played for Laughs several times in Mortadelo y Filemón. One of the most hilarious examples is when Mortadelo is ordered by the Súper to disguise as the latter in order to capture a killer who is attempting to assesinate the Súper. Filemón, oblivious to that, is ordered by Mortadelo to serve him a cup of coffee and a cigar -cue when he knows the truth to look really angered for Mortadelo, and once he finds him beats the shit out of his companion... just to find he actually beat the real Súper, who of course is not happy at all-
- At one point in The Blue Lotus, a man with a large, bushy beard and wearing sunglasses and a coat enters the bad guys' opium den and is immediately recognized by them as Tintin in disguise. Only when they beat him up, it turns out it isn't Tintin, just a man who happens to look like him with a large beard.
- Invader Zim: In Issue 38 of the continuation comics, GIR dresses up in a Dib costume, which somehow appears realistic enough to people that everyone except for Gaz become convinced that he's the real Dib and the real Dib is a clone. This leads to an angry mob chasing Dib out of town and into the woods, where he's stuck for the rest of the issue.
- In the Frozen fanfic Unfrozen, Elsa and Anna, having been pulled into Real Life circa 2013, suffer from this trope and are thought to be exceptionally good cosplayers by delighted parents. Elsa's (magical) snow is even mistaken for Practical Effects by Disney World employees.
- In the Buffy the Vampire Slayer/Angel fic Bring Me To Life, the Scooby Gang and Angel's crew are confronted by the newly-undead Lilah Morgan, reanimated as part of Wolfram & Hart's standard perpetuity clause. Buffy promptly assumes that it's the First Evil pulling a Dead Person Impersonation. Lilah proves that theory wrong by shoving a vase off of a nearby table, something the non-corporeal First would be incapable of doing.
- A Man of Iron shows Tyrion Lannister accusing the Small Council of dressing a whore as Sansa Stark, since she's a very grown-up, very living lady and poor Sansa was a dead teenager. How was he supposed to know the Night's Queen was able to bypass the Wall and remodel the corpse to her convenience?
- Alchemical Solutions has some people disbelieving Weaver when she claims to be Taylor Hebert in a mechanical body, due to the huge gap between awkward, average Taylor and brilliant, confident Weaver. It's more reasonable to assume a Tinker gave the "real" Taylor's template personality to a brand-new AI who later outgrew her settings.
- In Anastasia, the Dowager Empress Marie is thoroughly convinced that "Anya" is someone impersonating her long-lost granddaughter, even noting that "You're a very good actress." Her disbelief is understandable, since she has by this point already interviewed several girls claiming to be Anastasia.
- Justified in-universe since Anya is working with others to fool the Dowager, not realizing she actually IS Anastasia. So Anya herself thinks she is an impostor at first.
- In A Bug's Life, the ants and circus bugs build a gigantic bird costume (maybe the size of a sparrow or a robin) out of leaves and such to scare the grasshoppers away. Hopper figures it out, but then a real bird shows up...
Hopper: Well, what's this? Another one of your little bird tricks?
Hopper: Are there a bunch of little girls in this one, too?! Hello, girls!
- In the So Bad, It's Good comedy The Creature From The Haunted Sea, the main characters try to kill a Cuban guard and blame a sea monster. Guess what shows up...
- Early in Austin Powers: International Man of Mystery, Austin knocks out a waitress and pulls off a wig, revealing that "she" is actually a man (and one of Dr. Evil's henchmen). Later, when he meets Basil Exposition's mother, Austin knocks her out thinking that she, too, is a man in disguise, but it turns out that she is not an impostor and just looks "mannish".
- A similar thing to the above happened in the first Crocodile Dundee movie. On his first night in America, Dundee is in a pub and meets a 'girl' who turns out to be a transvestite. He cups the man's scrotum to verify this. Later at a party, Dundee meets someone he believes to be a man in drag, tries to find out the truth in the same way, and learns that it is, in fact, a woman. The woman does not seem to mind, and even looks very happy about it.
- In The Brothers Grimm, the titular brothers run a monster protection racket, and are called in to clear out another monster infestation... that isn't one of theirs. Their employer, of course, thinks it's their fault and plans to trap them.
- In Tombstone, Wyatt Earp enters a bar on his first arrival in town and introduces himself to the saloonkeeper...who seriously doubts that he is speaking with the famous Wyatt Earp.
Bartender: Milt Joyce, owner and proprietor.
Wyatt: Wyatt Earp.
Bartender: [snorts]... yeah, right...
- In the first Scary Movie, Buffy (who had inexplicably turned into an Alpha Bitch by that point) is killed while thinking the killer is Cindy disguised as him. Even after the killer beheads her, she still keeps ranting about the bad taste of the joke, much to his frustration.
- In Zorro, the Gay Blade, this trope is batted about a few times when the Spanish governor of Mexico hosts a masquerade ball in an effort to trap Zorro. The Alcalde is thrilled when Zorro appears and triumphantly rips off the hero's mask to find his best friend, Don Diego de le Vega (George Hamilton). Other guests arrive, all dressed as Zorro. De la Vega actually is Zorro, of course, but tampered with the party invitations to have everyone appear in a Zorro costume. Then when Zorro actually does appear...
- In Spider-Man 2, due to Power Incontinence the web-head must use the elevator to leave the building he's on top of. When someone else gets on the elevator, he just thinks Spider-Man is a guy in a spidey suit, and actually compliments Peter on the worksmanship. Peter plays along and thanks him, but also comments that it rides up in the back. Averted in the alternate version used for the Spider Man 2.1 cut where the guy assumes it's the real deal and tries to bring up new advertising techniques.
- In Days of Thunder after Cole Trickle wins his first race, his crew hires a stripper/prostitute to dress up as a state trooper and pull their motorcade over, where the woman fondles him, then takes off her clothes and presents herself to him. Later when Cole is in an accident and comes to in the hospital, he assumes the beautiful doctor (then-unknown Nicole Kidman) examining him is a similar setup.
- In The American President the titular character calls a lobbyist to see about arranging a date, only to be mistaken for a colleague who had wanted to give his Presidential impression. Said lobbyist has an Oh, Crap! moment when the President asks her to call the White House switchboard.
- In Pirates of the Caribbean: On Stranger Tides, Jack Sparrow is repeatedly mistaken for an imposter because everyone knows that "Jack Sparrow" is in London and gathering a crew to find the Fountain of Youth.
- Cleverly invoked in To Be or Not to Be, through a bizarre beard transfer between the imposter and the real, but dead Siletsky.
- In L.A. Confidential, Ed Exley thinks the woman with Johnny Stompanato is a hooker who has had plastic surgery to look like Lana Turner. It turns out to be the real Lana Turner who tosses her drink in his face.
- In Human Traffic, Koop's senile father suffers from an inversion of the Fregoli delusion (see Real Life); he thinks Koop is identical twins pretending to be the same person.
- In Sunset, Michael Alperin refuses to believe that Wyatt Earp is the real Wyatt Earp when Wyatt first introduces himself. (From the way he reacts, it's possible Michael thought Wyatt Earp was dead.) Leads to a funny And I'm the Queen of Sheba moment.
- The Archbishop of Canterbury in Johnny English, though in this case it was because Johnny had discovered the villain planned to have a henchman impersonate the Archbishop with a fake rubber mask. The villain, realizing that he had been found out, wisely decided to forego this plan, leading an unaware Johnny to humiliate himself in his attempt to remove the "mask" from the Archbishop's face.
- Played with in a string of elephant jokes.
Q: What did Tarzan say when he saw a herd of elephants in the distance?
A: "Look, a herd of elephants in the distance!"
Q: What did Tarzan say when he saw a herd of elephants with sunglasses in the distance?
A: Nothing. He didn't recognize them.
Q: What did Tarzan say when he saw a herd of giraffes with sunglasses in the distance?
A: "Ha! You won't fool me with those disguises this time!"
- The Baroque Cycle - Jack Shaftoe, a.k.a. King of the Vagabonds a.k.a. l'Emmerdeur, in rags and a slave collar rides a warhorse into a Parisian fancy dress ball (escaping captivity and trying to brazen it out) only to be mistaken for the king (of France.) Until the actual king arrives in his l'Emmerdeur costume, at which point all the noble women who'd been giving their jewelry to the 'fake' l'Emmerdeur feel foolish, and life becomes more exciting and dangerous for Jack (yet again.)
- In "The Brain Stealers of Mars", Rod Blake encounters a shapeshifting alien plant-thing that disguises itself—poorly—as his partner Ted Penton. He shoots it and it turns into a bat and flies away. He's still in the grip of hysteria when another Ted-Penton-thing shows up, and Rod shoots at it too. Of course, this one is real.
- A Certain Magical Index: When Thor first meets Touma, he uses magic to disguise himself as Mikoto to troll him. When Touma realizes the deception, he negates the disguise by touching Thor with his right hand. Later, Touma runs into the real Mikoto and mistakes her for Thor. He tries to negate the disguise again... by touching her chest with his right hand. Touma still doesn't get it even when "Thor" maintains the same appearance, and walks off while Mikoto is too stunned to react.
- Shows up a bit in G. K. Chesterton's work:
- In The Man Who Was Thursday, an actor named Wilks decided to parody "the celebrated Professor de Worms". He was too good and completely succeeded in convincing all and sundry that he was the genuine article. (The crippled de Worms was a less convincing cripple because Reality Is Unrealistic) Then the police recruited him, because the professor was an anarchist, and they needed someone to infiltrate.
Before I could fully recover, however, two or three of these admirers ran up to me radiating indignation, and told me that a public insult had been put upon me in the next room. I inquired its nature. It seemed that an impertinent fellow had dressed himself up as a preposterous parody of myself.
- Deliberately invoked in the Father Brown story "The Flying Stars". At a family gathering, the distant cousin suggests putting on a traditional English pantomime, and he phones his old friend to come play the role of the policeman. Soon enough, the old friend arrives in a remarkably realistic costume and he gives a spot-on reaction to all the slapstick that the distant cousin dishes out for him. And then the policeman turns out to be real, not an actor. And he came to arrest the "distant cousin", who's actually a notorious thief with a taste for theatricality. The thief suggested staging the pantomime specifically to provide a cover to beat his pursuer senseless and escape from the house.
- In "The Fairy Tale of Father Brown", this trope is central to the mysterious death of a Prussian Prince, twenty years prior. The prince, being very paranoid, had a lot of guards on his estate. That particular evening, the prince snuck out of the castle, alone, on some personal business. As he returned, one of his own guards mistook him for an intruder. Owing to a strange series of events, the prince had a gag over his mouth and couldn't remove it before the guard—following the prince's prior orders—shot him dead.
- In The Man Who Was Thursday, an actor named Wilks decided to parody "the celebrated Professor de Worms". He was too good and completely succeeded in convincing all and sundry that he was the genuine article. (The crippled de Worms was a less convincing cripple because Reality Is Unrealistic) Then the police recruited him, because the professor was an anarchist, and they needed someone to infiltrate.
- Wyrd Sisters plays with this: Death winds up filling in for the actor playing him in a play. People normally don't see him because of the Weirdness Censor, but now they're expecting to see Death... and he gets stage fright.
- Done intentionally by the wizards in Moving Pictures. Senior wizards can't be seen attending popular entertainment, so they need a disguise. And what better disguise than someone who's disguised as a wizard, because obviously that's not a disguise a real wizard would use. They even have false false beards (you take two bits of wire, stick them in your sideburns and hook them over your ears). Inevitably, the point arrives when they need to convince someone they're actually senior wizards, and can't.
- In The Light Fantastic, Death tells the wizards who summoned him that they called him out of a party. When they ask if it was a good one, he tells them that he expects it to go downhill at midnight. "'Why?' THAT'S WHEN THEY THINK I'LL BE TAKING MY MASK OFF."
- In the Judge Dee novel The Chinese Gold Murders, one character is a Master of Disguise who at one point pretends to be his brother's corpse. At the end, the Judge thanks him for scaring off enemies by pretending to be a ghost, and he tells the Judge he wasn't there and has no idea what the Judge is talking about.
- The Shirley Jackson short story "Louisa, Please Come Home" concerns a nineteen-year-old girl who runs away from home and returns three years later only to find that she Can't Go Home Again because her family thinks she's an imposter after the reward money. Dramatic Irony ensues.
- In a handful of Nancy Drew books where Nancy has had to contend with an impersonator, one of the many problems spawned from this has been people mistaking her for the double. Which is bad enough, but more so considering the nefarious things the other woman has been up to, such as theft or murder.
- Deliberately done by the superhero Dark Flame in Relativity. In order to sneak into a costume party, she removes her wig in order to look less like herself... and more like someone else dressed as her. It works.
- A Sweet Valley Twins book had the girls inverting their usual April Fools' Day prank, where they would switch identities. Unfortunately, they had played it so many times that no one was fooled anymore, leading Jessica to decide that they would not switch that year. . .only for everyone to of course assume that they had done so and end up making the girls miserable all day—Jessica was given all of Elizabeth's assignments and Elizabeth was dragged off to cheerleading practice, despite their repeated protests that they had not switched.
- Warhammer 40,000: Played for Laughs in The Last Ditch. When Cain note introduces himself to the freighter captain transporting the Valhallan 597th, the man cracks up laughing.
Course you are. Nice one. Bet the fems fall for that all the time, eh?
- A disloyal subordinate uses this against Tuon after Tuon's accidental abduction in The Wheel of Time - Suroth spreads rumors among the troops that some traitor is out in the countryside impersonating Tuon, and should be killed on sight. Since Mat keeps Tuon safe until her loyal bodyguard corps can return her to the capitol, it goes very badly for Suroth.
- This trope was played deliberately on Big Brother Australia. The housemates had to play as paparazzi and were shown celebrity impersonators whom they had to photograph. The Pamela Anderson impersonator turned out to be the real Pamela, and the housemates were genuinely surprised by this.
- At the end of an episode of Cheers, a patron comes into Cheers claiming to be Boston Red Sox star Wade Boggs. The gang assumes he's an impostor sent by rival bar, Gary's Olde Towne Tavern, to prank them, and bum rush the guy, dragging him outside and stealing his pants. When Carla rifles the guy's wallet, she finds his drivers license... which IDed him as "Wade Boggs". The gang decides this counts as a win, because they now have Wade Boggs' pants.
- Criminal Minds featured an episode ("Dorado Falls") where the UnSub developed Capgras Syndrome (see Real Life folder) after he sustained a head injury in a car accident. Thoroughly convinced that the government had replaced his loved ones and acquaintances with fake look-alikes, the criminal (a former marine that participated in Black Ops in South Africa) went into a killing spree, targeting his former boss, his parents and then his own family demanding to know what happened to the real them.
- On CSI, a Sherlock Holmes enthusiast who heads a club of mystery reenactors is murdered. When his fellow club members show up, they assume its a hoax set up by their friend. When Brass questions one member of the club, the member is told to 'drop the accent'. He replies that he can't, as he really is British.
- On CSI: NY, a badly-injured man who'd been buried alive staggers out of a cemetery and stumbles down the street, covered in blood and grave earth ... straight into a flash mob of people dressed as zombies. Nobody notices his genuine distress until it's too late, and he dies from his ordeal and previous injuries.
- Doctor Who: In "The Day of the Doctor", the Tenth Doctor is pursuing a shapeshifting Zygon in Elizabethan England. He first accuses Elizabeth herself of being the Zygon and is completely wrong. He then interrogates a rabbit before deciding it is, in fact, a rabbit. Then two Elizabeths appear...
- In an episode of The Drew Carey Show, Drew's brother faces termination for being a cross-dresser, just after being hired to work in the cosmetics department. Drew challenges fire-happy Mr. Wick to differentiate transvestites from actual women perusing the store. Wick believes he found a "bad" impersonator of Dionne Warwick, but it was actually her.
- Similarly, when Suddenly Susan and a male friend go to a gay bar, a patron compliments her—"That's a beautiful drag". She assures him that she really is a woman, but he scoffs, "Yeah, right. With those shoulders?" (She's also quite tall). It pays off when he picks a fight with her friend—he has no problem roughing him up, but immediately backs off when she comes to his aid.
- On Good Luck Charlie, PJ leads the other workers at Quickie Chickie on strike leading them to get fired. Bob dresses up like Corporal Chickie to try to get them re-hired. When the manager refutes "Corporal Chickie's" creds, another Corporal Chickie comes in, this time, the real one.
- In a Halloween episode of Hannah Montana, Miley (as Hannah) is mistaken for her evil identical cousin by her best friend, Lilly...who comments on how bad her imitation is.
- In an episode of Herman's Head, Louise answers the phone and laughs at the woman who says she's Maureen McCormick, better known as Marcia of The Brady Bunch. A minute or two later, Mr. Bracken storms out of his office and states that his good friend Maureen McCormick just called him and said that a woman with a voice like a cartoon character made fun of her. This doubles as a lampshade on the fact that Louise is played by Yeardley Smith, who voices Lisa on The Simpsons.
- In the JAG episode "Imposter", Clark Palmer had Rabb tied up in his apartment and impersonated Rabb in court to frame an innocent defendant in court with planted evidence. When Rabb eventually gets back to JAG the Marine security guards thinks he's the imposter.
- On Justified Dewey Crowe impersonates US Marshal Raylan Givens in order to rob a group of criminals who stole a shipment of Oxy from the Dixie Mafia. His plan goes without a hitch but the criminals soon realize that they have been conned and go looking for Dewey. However, Raylan gets there first and when he identifies himself, the criminals refuse to be fooled again and open fire.
- An episode of Law & Order: Special Victims Unit features a woman who, after a brain injury, has become convinced that her daughter isn't really her daughter. As a result, she doesn't notice that her daughter has been raped.
- The Science Fiction Sketch from Monty Python's Flying Circus plays with this a bit: A detective thinks that a blancmange-shaped alien is the notorious criminal Jack Riley, a blancmange impersonator and cannibal whom he'd encountered before, coming to the police office to turn himself in.
- In the NCIS episode "Witch Hunt", the team bursts in on a suspect, guns drawn, only to find a Halloween party in progress. The partygoers clap; one of them says, "Great costumes, but you misspelled CSI."
- In Ned's Declassified School Survival Guide, Cookie tries to get into the all-girls book club by dressing up as a girl, and Moze catches on. Then, when a teacher enters, Moze starts attacking the teacher, but finds out that the teacher really is a woman.
- In another episode, Vanessa tells Cookie that she has to take care of her grandmother, but he think's it just an excuse to get out of a date. At the end, an elderly lady in a wheelchair asks Cookie where Vanessa is, but he doesn't believe it and tosses the wheelchair down the stairs to expose it. Only then does Vanessa appear beside him.
- The New Avengers: In "Faces", both Gambit and Purdey go undercover to infiltrate an organisation that is creating duplicates of intelligence operatives, where they are employed as doubles of themselves. Each ends up believing that the other is an imposter, and has killed the real Gambit/Purdey.
- Goes badly in Only Fools and Horses when Del hires a stripper to pretend to arrest his uncle for his birthday. After his car is seen driven erratically (by Rodney) Del assumes the policewoman who come to question him about the incident is revenge. He is arrested for indecent assault.
- The Sarah Palin opening sketch on Saturday Night Live where Alec Baldwin mistakes Palin for Tina Fey (see Real Life, below).
- In the Sherlock episode "The Empty Hearse", an eccentric DVD-seller comes into John's surgery and John thinks he's actually Sherlock in disguise. He isn't, but the scene pays homage to a scene in the equivalent short story, where Holmes turns up at Watson's house disguised as an eccentric bookseller.
- Supernatural features a writer who gets visions of Sam & Dean's adventures and uses them for plots in a series of books called "Supernatural." Sam & Dean get tricked into attending a convention for his fans, where almost everyone male is LARPing as them, and are forced to masquerade as just really obsessed fans in order to stop an actual ghost without interference. But later, two of the fans find out some of the secret and volunteer to help, despite the danger unwittingly telling Sam & Dean that it's what Sam & Dean would do. Then everyone who works at the hotel and all the fans witness the ghost attacking them, forcing them to accept the supernatural, but luckily for all involved, the author saves them.
- In an episode of That's So Raven, a dog follows Cory home and Victor puts up "Lost Dog" posters to get whoever owns the dog to come to the house and pick him up, but Cory grows to love the dog and takes them down. Later, an intellectual kid named Chauncey arrives claiming that he came to pick the dog up, but Victor think it's Cory in disguise and attacks him... only for Cory to walk into the room. Bonus points for both of being them played by the same actor.
- The Thin Blue Line: after a succession of student pranks for Rag Week, Inspector Fowler single-handedly arrests (and insults) a group of armed, masked bank robbers, assuming it's another joke.
- In Anything Goes, Bishop Henry T. Dobson boards the ship while Moonface Martin is also on-board masquerading as the ship's chaplain. The local authorities are warned that a criminal is masquerading as a priest and, predictably, haul off the protesting Bishop.
- In Cash on Delivery, Eric Swan has coerced his friend and roommate Norman to dress up as a woman, whereupon the head of the Social Security, a female, shows up unexpectedly. Eric, thinking that the woman is a dressed-up Norman, proceeds to not onyl comment on how Norman "made the breasts too big" but proceeds to juggle and motorboat said mammaries.
- A variation in Little Me: On a sinking ship, Noble Eggleston continually confronts the captain, who is trying to flee by disguising himself as a woman. Around the third time or so, he confronts the captain again, but this time it's actually a woman. He apologizes to her, saying, "I'm terribly sorry, madam. The captain wears the same kind of dress."
- In "Nothing's On", the play-within-a-play in the comedy Noises Off, a sheik comes to look at the house where a series of misunderstandings have led everyone to be very angry at the man of the house. Unfortunately, the sheik and the house owner are identical strangers (which the director sarcastically chalks up to the long-lost prequel). The sheik is promptly accused of trying to avoid "his" (the house owner's) lumps by donning a ridiculous disguise.
- In [PROTOTYPE], one of the abilities Alex Mercer gains is "Patsy", faking out the military by accusing one of their own of being a shapeshifting mutant. And, of course, since Alex himself is the shapeshifting mutant they're hunting...
- In Suikoden V, Euram falls for one of these. The main character from the second game has that happen to him when you recruit Hoi (a actual imposter of the hero) he gets actually beat up by a angry bunch of villagers along with the real imposter
- In the online game Legends of Zork, at the end of the quest "Antharia Jack and the Hat Mislaid", it turns out you've been trying to find Antharia Jack's hat for a crazed fan rather than the real Antharia Jack - and furthermore, there's an entire fan club in town devoted to dressing up like him. This culminates in you irritably pushing aside the real Antharia Jack, who comments that it's been the third time it's happened to him that day.
- In a sidequest in Paper Mario: The Thousand-Year Door, Mario is given the task of helping a die-hard Luigi fangirl meet the man himself. Unfortunately, Mario's brother is unavailable, so Mario has to dress up as Luigi and meet the fan instead. While he is doing so, the real Luigi shows up and the obvious happens. Made worse by the fact that Luigi asks Mario to back him up, only for him to play dumb about it.
- The penguin detective also thinks that Mario, in his regular clothes, is Luigi, no matter who tries to correct him. When Bowser shows up and tries to intimidate the detective into handing over the Crystal Star, he is thus told that Luigi has already made off with it. He doesn't take it well.
- Near the beginning of Super Paper Mario, Mario visits a wizard to get a new power, only for the wizard to assume he's an impostor because his appearance matches that mentioned in the Light Prognosticus prophecy.
- In Tales of Monkey Island Chapter 2: The Siege of Spinner Cay, when Guybrush thinks the human LeChuck is an impostor:
Guybrush: Sooo... you say you're human now, huh? Well, [snaps his finger] let's just see what happens when I ...PULL OFF YOUR MASK!! [jumps at LeChuck's face]
LeChuck: Owwch!! Guybrush, stop that! [pushes him off]
Guybrush: [understands] Huh. Okay... maybe you are human. I still don't like you.
LeChuck: Be that as it may, we still must work together to retrieve this Summoning Artifact!
- In the Meet the Spy trailer for Team Fortress 2, the BLU Soldier is convinced that the BLU Spy is actually a RED Spy infiltrating the base, and sees fit to prove it the quickest way possible. Unfortunately for the BLU Spy, he was wrong.
- In Professor Layton and the Diabolical Box, when Layton and Luke find what they think is Dr. Schrader's dead body, Inspector Chelmey arrives. In the previous game, Curious Village, Inspector Chelmey turned out to be Don Paolo in disguise. So as soon as he sees Chelmey, Luke tries to pull off his 'mask'.. only to find out that it's the very real, and now very angry, detective inspector.
- Night Trap: In the "controversial" bathroom scene, when Lisa hears an auger in the shower, she thinks the auger is Megan in a "scary costume" and opens the shower door in an attempt to get it out; but when it starts coming for her, she gets an "Oh, Crap!" look and tries to escape but is cornered by two more augers... and that could be the end of her if not for the floor trap near the shower that the auger is getting on (provided that you need a special code to activate the trap and save her in time).
- Inverted if you try to catch one of the "augers" on one occasion... without even knowing that the "auger" is actually Token Black teammate Eddie in disguise.
- The clones from Dark Legacy Comics don't understand Halloween, and spend the day unmasking the other characters in their costumes, by pulling off their fake heads. They then meet a real Pandaren Monk, hilarity and a real painful death ensue.
- In Multiplex, former Multiplex employee Brian isn't able to pull off his robbery plans because Kurt, who's manning the register, immediately assumes that being held up at gunpoint is just the latest iteration of the ongoing prank war between himself, Melissa, and Jason. He doesn't stop laughing until the robber panics and leaves, at which point the rest of the cast clues him in.
- Used to some extent in this xkcd comic. Which could also be used to illustrate the trope.
- In Yet Another Fantasy Gamer Comic, the new Drow jester does a great Alzaer'bith! At least, she adapts, "drinks on me" being the nicest thing she heard in a long time.
- In the SuperMarioLogan episode, "Jeffy's Tantrum!", Mario refuses to buy Jeffy a Spongebob Squarepants game on the App store with his credit card, so Jeffy decides to run away. The doorbell rings, and Mario comes across who appears to be Jeffy wearing Groucho Marx glasses, asking for his credit card number. Mario thinks it really is Jeffy, so he refuses to tell him his credit card number, and tells him he's not fooled by his disguise. Who appears to be Jeffy tells Mario he doesn't know what he's talking about, and the real Jeffy shows up, asking Mario who the guy who looks like him is.
- Donald Duck
- In the cartoon, "Donald Duck and the Gorilla", Donald's nephews pretend to be an escaped killer ape to scare Donald. He catches them, and when the actual killer ape shows, he slaps it around a few times before realizing what it is and running for his life.
- In the cartoon "Lion Around", two of Donald's nephews dress up in a lion costume to scare Donald while the third nephew goes for a yummy pie. However, one slip-up has Donald discover who the "lion" really is and shoos the nephews out of the house. Then a real mountain lion shows up and goes to Donald's house in an attempt to eat him and the pie. However, Donald thinks the actual lion is just his nephews in costume and tries shooing it away, but the lion persists and enters his house. At once Donald becomes infuriated and even attempts to rip off the lion's head, but then one of his nephews knocks on the window and tries convincing Donald that the lion is real by showing him the costume, which the nephews had taken off. It takes Donald a few seconds to realize that the "lion costume" he attempted to "take off" is actually a real lion, whom he had just ticked off! Oh, Crap!!
- In the DuckTales (1987) episode, "A Drain On the Economy", the Beagle Boys disguise themselves as a Sewer Gator to scare off Scrooge's nephews. Then the sound of an alligator growling can be heard, and Big Time tells the other Beagle Boys to stop fooling around. The other Beagle Boys tell him they aren't fooling around, and point out the real sewer gator behind them.
- In the Family Guy episode, "Business Guy", Lois gets her father, Carter to dress up like a Swamp Monster to trick Peter into signing Pewterschmidt Industries back to him. At first, this example appears to be averted, but then the real Carter shows up in a Swamp Monster costume and he and Lois run away from the real Swamp Monster who is later revealed to be a disguised Gregory House.
- In a similar, though more comedic vein to Supernatural, Filmation's Ghostbusters does this at least a few times. The funniest is in "The Phantom of Vaudeville". The titular phantom mistakes the Ghostbusters as a comedy duo who'd stolen his act many years before—the kicker is that the duo actually existed, and had a third banana in the form of a man dressed as an ape (in the context of the show, Tracy is a real gorilla). When the Phantom tries to forcibly unzip Tracy's "costume", he gets a... shall we say, less than pleased gorilla on his hands.
- The first episode of The Flintstones had Fred thinking Barney was throwing a party without him. In response he tells a friend to dress as a police officer and come to the party complaining about the noise. Said party turns out to be a surprise birthday party for Fred, who quickly gets into it. Naturally, the noise gets too loud, and a cop shows up...
- It's done in Garfield's Halloween Adventure. The first time Garfield does that, it's just a kid in disguise. The second time... it's a scary monster disguised as Bedsheet Ghost. The third time... a monster wearing a mask that looks just like its face. The fourth time... a Bedsheet Ghost with, well, nothing under the "bedsheet".
- In the Hey Arnold! episode "Ghost Bride", this happens with two separate impostors before the real ghost shows up.
- Inspector Gadget, in his usual fashion, did this. In "The Infiltration", which involved Master of Disguise Presto Change-o, Gadget tried to pull off a young woman's very pretty face; he believed she was Presto in disguise.
Gadget: All right, so perhaps I was mistaken. I assure you it won't happen again! But if I don't find Presto Change-o soon, the security of the free world could be in jeopardy.
- Jimmy Two-Shoes: In "Best Bud Battle" (where Beezy and Heloise fight over whose house Jimmy gets to stay at for the episode), Lucius comes to Heloise's house when she has Jimmy to go over something work related with her. She mistakes him for Beezy in disguise, and launches him into the sky. A big case of Idiot Ball, since Heloise would usually be smart enough to realize that Beezy is too big to pose as Lucius.
- In Episode 65, Kaeloo sees Mr. Cat disguised as Pretty and takes a while to realize that it was a disguise. She then looks around, finds the real Pretty, and tries to yank her face off thinking it's a disguise.
- In Episode 83, Stumpy waits for a long time for his girlfriend Ursula to show up to a party. When the party is halfway over, he wonders why she hasn't come yet, and gets the idea that maybe someone at the party is Ursula in disguise. He then decides that the imposter must be Pretty, so he tries to pull her face off, thinking it's a mask.
- Looney Tunes:
- In the short Picador Porky, Porky enters a bullfighting competition and has two friends dressed as a bull for him to fight. The friends get drunk and wander off, so Porky ends up fighting the real bull. It's only when the two guys appear singing drunkenly on the sidelines that Porky realizes the trouble he's in and starts running.
- In Stage Door Cartoon, Elmer Fudd is stripped of most of his clothes by Bugs Bunny, and when he is about to gives chase, an officer shows up to arrest Elmer for indecency. However, as the officer is dragging Elmer away, he gets sidetracked by the Bugs Bunny cartoon that's playing and forces Elmer in so he can watch. In the cartoon-within-the-cartoon, Elmer sees Bugs dress up as an officer that looks identical to the one sitting next to him. Realizing the implications, he rips off the "officer's" disguise... only to find out that he's a real human police officer, resulting in Elmer getting into even more trouble.
- In Big House Bunny, Bugs disguises himself as a prison warden to trick guard Yosemite Sam. Once Sam sees through the disguise, he chases Bugs out of the office and back in again, and ends up clubbing who he thinks is Bugs over the head. He then learns, to his utter horror, that he just attacked the real warden!
- Played with in the Phineas and Ferb episode "Get That Bigfoot Outta My Face". At one point, the titular characters rig up a false Sasquatch to scare their friends and Candace; when a much more realistic Bigfoot shows up, Candace runs it down talking about how clearly it's fake, then the kids run in terror when she is eaten by it. Turns out, though, that Candace, her grandparents, and her grandmother's identical twin had put it together as a prank of their own.
- An episode of Pinky and the Brain has the duo grow to gargantuan size, while Pinky wears a Gollyzilla costume. Brain hopes to let Pinky "rampage" a bit, and then come out to save the day. Unfortunately, Brain runs into the real Gollyzilla.
- A good number of the Scooby-Doo movies have a mundane impostor followed by a real supernatural entity.
- In The Simpsons, Homer annoyed Moe one too many times, and Moe kicked him out of the bar. Soon Homer reappears, dressed in a top hat and natty suit, sporting a handlebar mustache, calling himself "Guy Incognito." Moe beats him up and kicks him out of the bar again (in an unconscious state), only to have the real Homer show up and remark on the uncanny resemblance.
- Spongebob Squarepants
- In one episode SpongeBob sees a gorilla attacking Sandy and concludes that it must be Patrick in a costume, and then Patrick walks up. However, the gorilla takes off its mask to reveal the real Patrick, and other Patrick takes off its mask to reveal a gorilla.
- In the episode where Mrs. Puff is in jail and she likes it better than teaching at boating school, SpongeBob and Patrick tried to break her free. Of course, Mrs. Puff didn't want to leave. One of their attempts to get her out was donning perfect disguises of prison guards. After they left, two real guards came to see Mrs. Puff. Thinking that they were Spongebob and Patrick wearing disguises, she pulled off their faces.
- On two occasions, SpongeBob is being kicked out of some place: the first time it was a tough-guy club and the second time it was a slumber party. Each of these times, someone who looks a lot like SpongeBob shows up. In the first instance, the bouncer tries to pull off SpongeBob's wig (the preceding scene suggested SpongeBob to get a new haircut) which looks like black greaser hair, only to see the real SpongeBob show up in a blatantly obvious rainbow wig, and let the Mistaken for an Imposter person inside. In the second, it is a girl who wants to go to Pearl's party, but is kicked out because the partygoers are annoyed with SpongeBob. She runs off crying, and SpongeBob comments, "Whoever that was, she was uuugly!"
- SpongeBob also does this to Mr. Krabs when Plankton replaces him with a robotic suit. For some reason SpongeBob is unable to tell the difference between the real Mr. Krabs, and the robotic Mr. Krabs. Keep in mind the robot constantly acts like a backfiring truck, talks in a robotic voice, and acts very suspiciously. Then again, it's SpongeBob.
- "Nasty Patty" has SpongeBob and Mr. Krabs wrongly assume that a health inspector at the Krusty Krab is actually a con artist trying to scam his way into free meals. They eventually realize their mistake when the news reports the con artist was captured... after they'd seemingly accidentally killed him by serving him a revolting Krabby Patty.
- Steven Universe: In "The Big Show", at Sadie Killer and the Suspects' performance in Empire City, Sadie sees a woman in the crowd who she assumes to be her mother, Barb, in a Paper-Thin Disguise. After the show, the woman comes backstage to meet the band, and Greg introduces her as Sunshine Justice, the owner of the venue. Sadie is surprised to realize she actually wanted her mother to come to the show, and decides to invite her to the band's next one.
- In an episode of Strawberry Shortcake, Custard and Pupcake dress up as crows in hope of faking out a fairy who was Playing Sick. It doesn't work, but later, when a real crow shows up, the fairy derides it for trying to trick her again, and she even pulls out a feather before realizing it's the real thing.
- Tiny Toon Adventures:
- Buster spends the majority of the short, "Ruffled Ruffee" from the episode, "Music Day" spoiling a children's concert hosted by the Raffi Expy Ruffee, while dressed in a diaper and a green bonnet. When Ruffee finally does reach his breaking point, he yells at who appears to be the disguised Buster, but when he picks him up, he's actually a human baby dressed in a nearly identical way. This proves to be a big mistake when said human baby's oversized father scolds Ruffee for doing so, and later beats him up.
- In the first wraparound of the episode, "Stuff That Goes Bump in the Night", Babs scares Buster by dressing like a devil. In the third wraparound, a Two-headed Monster sneaks up behind Buster, who thinks it's Babs in disguise again. The real Babs shows up, and the two bunnies run for their life from the Two-headed Monster.
- Tom and Jerry: In Fraidy Cat, Jerry spooks Tom by, among other things, covering a vacuum cleaner with a white sheet and turning it on to make it look like a ghost. After Tom grows wise to Jerry's tricks, he sees Mammy Two-Shoes walking around in her nightgown and, thinking it's Jerry pulling the vacuum trick again, pounces her and bites her in the rear.
- In Yogi's Great Escape, Yogi and his friends keep trying to scare away ranger Smith and a trapper accompanying him by dressing up as a ghost. Later on, when the ranger corners Yogi in a room, a real ghost shows up and Yogi assumes it's someone else in a costume.
- Yogi's Space Race: In Galaxy Goof-Ups, a villain wants to capture the Goof-Ups for his private zoo and lures them into a trap. Captain Snerdley tries to warn them but they won't listen because they think he's an imposter.
- Quite a few celebrities attending conventions like Comic-Con have been mistaken for cosplayers.
- There is a disorder known as Capgras delusion, which causes the person affected to believe the people closest to them have been replaced by impostors. Inverted with the Fregoli delusion, where you believe multiple people are actually the same person in different disguises.
- Charlie Chaplin entered a Charlie Chaplin Impersonation contest.... and came in third.
- The contest was to impersonate the Tramp, one of Chaplin's most popular characters. The judges noted his perfect impression, but he lost points for showing up on the spur of the moment with no costume.
- Larry the Cable Guy had a similar experience in Las Vegas at a club where people did celebrity impressions. He played himself, and interviews of people leaving said he did the jokes well, but didn't sound the same.
- An audience member was asked to leave a showing of The Rocky Horror Picture Show because he was a Tim Curry impersonator. The member: Tim Curry himself.
- Similarly, Christopher Walken once had a guy in a diner say to him: "quit doing that stupid Christopher Walken impersonation. It's getting annoying."
- When appearing at science fiction conventions, Claudia Christian of Babylon 5 fame will often recount the story of how she once attempted to join a B5 discussion group, only to be chased off by the regulars as an allegedly clumsy and unconvincing impersonation!
- In the 60's, Brazilian rock'n'roll musician Raul Seixas once showed up to perform so high that he couldn't sing his own songs. That led to the audience thinking he was an impostor and calling the police.
- Dolly Parton once lost a Dolly Parton look-a-like contest. It gets better: the other contestants were all drag queens.
- The late Jeremy Beadle hosted a hidden-camera prank show called Beadle's About during the 1990s. He would appear in disguise (usually as an authority figure like a policeman or traffic warden), wind up the victim a little more, and then reveal that it was all a set-up for the TV. The downside? There was at least one case of a member of the public mistaking a real policeman for Jeremy Beadle, and attempting to pull his "disguise" off ...
- Similarly, Candid Camera host Alan Funt was once on a flight that was hijacked and flown to Cuba. Because everyone on the plane recognized him, he was the only passenger to realize that this wasn't a joke.
- In 2008, Tina Fey became famous for playing Sarah Palin in a Saturday Night Live skit. When the real Sarah Palin later appeared on the show, she was briefly mistaken for Tina Fey.
- Minecraft servers often get players logging in, claiming that they are one of the game developers. This led to an incident where jeb_ joined a server, only to be told that he's "not the best fake I've ever seen".
- Both Brian Cranston (Walter White on Breaking Bad) and Hugh Jackman (Wolverine) have told stories about attending ComicCon and being ignored by going in costume as Walter White and Wolverine, respectively.