Because I'm Jonesy

When an imposter is spotted because the person he's impersonating is in the group/room with, or is himself, the person they're trying to deceive. In its basic form, the conversation will go like this:

"Stranger: Who are you? Master of Disguise: I'm Jonesy. Stranger: No you're not. Master of Disguise: How do you know? Stranger: Because I'm Jonesy."

"Jonesy" comes from this page (and the one before it) of The Adventures of Dr. McNinja #1.

If you have a good enough disguise, you might still be able to get away with bumping into the person you're impersonating if you convince them that you are actually their reflection in a mirror. Those liable to Pretender Diss are also generally vulnerable to this.

Compare I Am One of Those, Too, I Am Spartacus.

And no, the trope is not named after Jonesy Garcia.

Anime and Manga

 * Baccano! has an instance of this involving a member of the white suits. Would not have been so bad if the person he was trying to trick was.
 * Subverted in the 8th Detective Conan movie, where Kaitou KID shows up disguised as Shinichi. Conan, who is standing right there, immediately blurts out "That isn't Shinichi!", but has no evidence to back it up without giving away his secret identity. He can't use the usual proof of tearing off Kid's mask because Shinichi and Kid share the same face.
 * A major plot point in Eyeshield 21 is when the titular running back comes across the "real" Eyeshield 21.
 * And later
 * This happens quite often in Fist of the North Star, but most memorably when Kenshiro (the title character) faces Jagi. Generally, punk X would have his henchmen kicking around peasants in the name of the Fist of the North Star. Then Kenshiro walks into town, and the henchmen make the mistake of asking him to bow to the Fist. Kenshiro makes a rude comment about how it's a terrible likeness, or asks a rhetorical question about the technique that he is supposedly about to be punished with ("you mean THIS hundred crack fist... WATATATATA!"). Henchmen try to punish Kenshiro like they do the peasants, and of course a righteous ass kicking ensues. By the end of the confrontation it's pretty obvious who the true Fist is.
 * Appears in the 2003 anime version of Fullmetal Alchemist anime with the fake Elric Brothers.
 * This happens in the first episode of Naruto between Iruka and Mizuki. Mizuki is in Iruka form, and Iruka is in Naruto form. The fake Naruto attacks the fake Iruka, and it's revealed he knew Mizuki wasn't Iruka because HE was Iruka.
 * In the first episode of Rurouni Kenshin, a small-time bad guy is killing people, claiming to be the infamous Hitokiri Battousai, and loudly proclaims he uses the style of the Kamiya Kasshin school, which the bad guys are trying to take away from its owner Kaoru. When Kenshin, the true Battousai, shows up, not only does he kick the fake Battousai's ass, but he reveals the true style of the Battousai—Hiten Mitsurugi, a style developed during the violent upheaval that ended recently unlike Kaoru's style, which was developed in the current time of peace
 * This happens in both the in animefiller and the manga in Saiyuki. In the anime the sanzo party . And in the manga when the sanzo group were made to face off against Shikigami doppelgangers of themselves.
 * Happens frequently early on in Trigun almost exactly like in Fist of the North Star above, some goon is using Vash's name to cow a town into submission, Vash shows up, disarms the goon, and is regaled as a hero. Unlike Fist (and most other examples) it's rarely revealed that Vash IS The Humanoid Typhoon (to the townsfolk anyway) but he still makes it fairly obvious the goons aren't the real deal.
 * Has happened a couple of times in Lupin III, thanks to Lupin's favorite disguise being his own archnemesis, Inspector Zenigata.
 * The major plot point of the very first issue of Fairy Tail. Long story short, the real Natsu confronts an imposter using illegal magic in his name.
 * This trope is what does in Master of Disguise Saemon from Basilisk, as his disguise as Tenzen is exposed by the actual Tenzen in some rather unfair circumstances.
 * During one of the picture dramas for Princess Principal, Woman of a Thousand Voices Beatrice impersonated Ange while calling Princess so that Beatrice could find out whether Princess thought Beatrice was a liability to the team – not knowing Ange was standing beside Princess at the time. Princess played along.

Comic Books
""Lay off the kid, he's not Venom!" "How do you know, Clark?" "" (attacks)"
 * Spider-Man and the first appearance of the Chameleon, though he has to make up another excuse as to how he spotted the impostor pretending to be Peter Parker to avoid revealing his secret identity.
 * Another exchange:


 * In the "Where Were You on the Night Batman Was Killed?" arc in Batman #291-294, the Riddler disguises himself as Bruce Wayne to crash a party his gang was robbing. This naturally surprises Batman when he arrives to stop the gang. He later claims that he recieved a phone call from Bruce Wayne in Florida earlier in the evening and thus knew that the Riddler wasn't the real Wayne.
 * From the 1940's newspaper comics, Batman disguised himself as a mob boss... whose henchmen had just decided to get rid of. After being held at gunpoint, the real mob boss comes through the door. Hilarity Ensues.
 * In The Sandman, a reporter infiltrates the "Cereal Convention," a convention for serial-killers from around the world, by posing as the Candyman, one of its attendees. He hopes to promote his newspaper, which is focused on the exploits of the attendees and those like them, and also to gain new insight and understanding into their work. Unfortunately for him, not only is he an unconvincing actor but the Corinthian, an actual nightmare, knows for a fact that the Candyman died last year, killed by the Swamp Thing. As one would expect from a convention of murderers, rapists, kidnappers and people who talk at the theater they do not let his deception go unpunished.
 * In a Bronze Age Superman story, Superman is captured and, while escaping, encounters his friends Lois Lane, Jimmy Olsen and Perry White who claim be being held prisoner as well. He realises that these are actually robot doubles planted by his captor when he sees the remaining two prisoners: Morgan Edge and Clark Kent.
 * In one issue of Marvel Comics G.I. Joe series, Master of Disguise Zartan infiltrates the Pit, and moves about shifting his appearance from one Joe to another as he goes. However, he shifts into looking like Gung Ho just as the real Gung Ho enters the room; alerting the Joes to the fact that one of them is an imposter.

Film
"Herod: Mr. Hanlon, I want to ask you about Indian Wells. Did that fight really take place? You really killed four men? Hanlon: (smiles) Two with my right hand, two with my left. Truth be told, I'm equally good with either. Herod: You must be the fastest gun in the west. (Beat) That, or the biggest liar. Hanlon: (his smile suddenly fades) A pity you weren't there to find out. Herod: Oh, but I was, Ace. See, I was the one who really killed the Terence brothers, and I doubt a lying little chicken-shit like you was even in the same state! Hanlon: (is now visibly worried)"
 * In the X-Men films, Mystique does something similar to this with Lady Deathstrike and an office janitor.
 * She later
 * In the 1939 film version of The Hound of the Baskervilles, Watson tries to intimidate a mysterious peddler into talking by claiming, dramatically, "I'm Sherlock Holmes!" The peddler straightens to Holmes's full height and replies, laughing, "Then my name must be Watson!"
 * In Jackie Chan's Drunken Master the protagonist Wong Fei-Hung tries to trick a middle-aged man he sees eating alone at a inn into paying for his overly-large meal, when he tries to leave however, he runs into the manager who inquires as to who will be paying the bill, Wong says the middle-aged man will, at which point the manager asks Fei-Hung what his relation to man is, Fei-Hung states that the man is his father, at which point the manager informs him that the middle-aged man is really the inn's owner and that he is his son and that he's never seen him before.
 * In the 1995 The Quick and the Dead, John Herod is hosting, as well as competing in, a gunfighting tournament. One of his opponents is Ace Hanlon, a man with a few tricks, but whose guns aren't quite as quick as his mouth. As their fight is about to begin, they have the following exchange:


 * In Taking Care Of Business, Jimmy Dworski escapes from jail, finds the Filofax of Spencer Barnes, then impersonates Barnes until the real Spencer Barnes shows up.
 * A variation. Near the end of Batman Begins,

Literature

 * In the short story "Animal Rescue" (later expanded into novel The Drop) by Dennis Lehane, a small-time thug had a scary reputation based on the rumor that he'd killed a fellow named Richie Whelan a few years back. The police never pinned it on him, but he used this to intimidate people ... until he tried to push around, one of the guys who really murdered Richie Whelan. Oops.
 * In the short Lord Peter Wimsey story "The Bibulous Business of a Matter of Taste", several men all claim to be the aristocratic sleuth and wine expert Lord Peter Wimsey. A wine tasting is held in order to determine the real Wimsey. Their host can't figure out who the real one is until
 * In East of Desolation by Jack Higgins, narrator Joe Martin is hired to help with the investigation of a small plane that crashed. The pilot's widow, Sarah Kelso, comes along ... only she isn't, because Joe flew that plane under a false name, since he'd suspected (correctly) there was something dodgy about the job. And he'd never in his life seen "his widow" before she turned up along with the investigators.
 * Jennifer Government, the subplot about Billy NRA. When the real Bill NRA finds out, he attacks Billy, and the ensuing fight attracts the guards.
 * An amusing variation—more a case of "Because He's Jonesy"—is pointed out in Jim Lovell's autobiographical novel Apollo 13 (originally Lost Moon). Lovell is traveling to a hotel in Houston under the name of Max Peck, to receive his new assignment as a NASA astronaut. Shortly after he settles in to his room, he gets a call from another guest, who also claims to be Max Peck. Lovell, at this point, realizes there is probably more than one ersatz Max Peck here, because he had picked up another bit of info on the way to the room: "If you have a problem, take it up with the manager. I understand his name is Max Peck!"
 * A Real Life example, as the book is largely nonfiction. The scene is repeated in the television miniseries From the Earth to the Moon, including a very puzzled check-in lady who is NOT in on the fiction.
 * The Codex Alera has the "Because you're Jonesy" variant. Aldrick ex Gladius, regarded as one of the greatest swordsmen in the world, is famed partially because of his legendary duel with Araris Valerien, which is still being talked about fifteen years later. At multiple points throughout the series he crosses swords with other famed warriors, calmly informing each of them "The only man who has ever matched me in battle was Araris Valerian himself, and you aren't Araris." At the climax of Furies of Calderon, it turns out his opponent is Araris. Aldrick practically collapses when he realizes this.
 * In The Bad Bunch by J. T. Edson, Belle Boyd poses as Belle Starr in order to infiltrate an all-female outlaw gang. Unfortunately for her, the real Belle Starr had the same idea

Live-Action TV
"Barmy: Mr. Wooster's residence. [pause] Where is Mr. Wooster? He's not at home, sir. I'm Jeeves. [pause] What do you mean 'you think not?' [pause] Oh! [He hangs up.] Bertie: Who was it? Barmy: Jeeves!"
 * A variation in an episode of Xena: Warrior Princess had a cocky wannabe bandit try to intimidate Xena by telling her that he had killed the dread warlord somebody, which earned him only a passing nod. Later on, he repeats the boast, and Xena tells him he's a liar, and he didn't kill that guy. "How do you know?" "Because I did."
 * The first episode of the children's show Ghostwriter featured one character infiltrating a gang that wore doubleface masks when stealing and had code names based on characters in their favorite videogame. During the meeting the group introduced themselves with the names—the infiltrator had a fifty-fifty chance of picking the name the unintroduced gang member didn't have. He chose poorly.
 * In an episode of NCIS: Los Angeles, Callen poses as the backup for a member of a team of hired assassins, whom the rest of the team would not have met, telling the others that his partner missed his check-in call, only to find that, despite the captured assassin supposedly calling his backup to check in, said backup is already there.
 * In Jeeves and Wooster season 1 episode 5, "Brinkley Manor," Jeeves is away and Bertie is forced to take care of himself. While he is struggling to make tea, Barmy Fotheringay-Phipps arrives for a visit. When the phone rings, Bertie asks Barmy to answer it and pretend he is Jeeves.


 * Averted in Highlander. In "The Messenger", the real Methos did turn up to confront the false Methos, and asked some questions, but he never revealed he really was Methos.

New Media

 * A (The Customer is) Not Always Right entry has an interesting variation on the tell. A man comes in and orders a drink. When asked to pay up, he claims to be a close friend of the manager, who said the barista could hook him up with a free drink. While he's trying to swing his story, another guy comes in, to whom the barista cheerily hands a drink, free of charge. "Oh, so I can't get a free drink, but that jerkoff can?" "Sir, it's not polite to call your close friend a jerkoff."
 * This is arguably the straightest example. Bonus points for using an ID they didn't bother to check.
 * And invoked here.
 * And here.
 * This Hey Weiner entry.
 * There's a variant in a joke floating around the internet where a guy gets taken to a mental hospital because he's convinced that Jesus sent him on a quest of some kind. When he says this in the waiting room, another patient jumps up and calls bullcrap, because he (the second patient) did no such thing.

Tabletop Games

 * Forgotten Realms had a wizard and Harper agent Nleera Tarannath playing one of Tesper family ghosts, quietly observing or contacting people on each party for seven years. Until the smiling real ghost appeared right next to her before the lord Tesper. In this case, she was allowed to continue the game. Though after a year of this she took to visit the place with her own face, as his fiancee. Ghosts blew her cover on purpose, to push them together a little—once they were sure she's fit for their descendant, that is.

Video Games

 * Spies in Team Fortress 2 are easily rooted out by the people on the other team whose names the game has randomly given them for their disguise.
 * Or, in a much easier sense, if a player knows he's the only person on his team with his class (in which case the Spy will inevitably have that player's name).
 * The Halloween update had a "Costume Contest" achievement for killing Spies disguised as your class. Spies themselves have an achievement (Identity Theft) for killing the guy they're disguised as.
 * In Metal Gear Solid 2, Pliskin knows that the person claiming to be Solid Snake is, in fact, an imposter. Wonder why? Ah, it's the voice. He doesn't have the sexy manliness of David Hayter.
 * In Solar Winds, you're given a display filter so that aliens you talk to over video communications will see you as being one of them, and thus won't attack you on sight. Unless, of course, you run into the specific alien the display filter was recorded off of, who recognizes your treachery and tries to blast you out of the sky.
 * In one of the missions in Hitman: Contracts, you have to disguise yourself as a waiter to infiltrate a party. However, it would be a very good idea to knock out the real waiter first, or else the security guards will easily catch on when they see too many waiters running around.
 * In Thief 3, you overhear a conversation in which a guy is obtaining a lucrative contract by pretending to be you. True to the game's minimal-violence style, you also hear where he will stash the loot, so you let him do the work and then steal it.
 * In Suikoden II the Hero catches someone pretending to be him.

Web Comics

 * The Trope Namer, as noted above, is The Adventures of Dr. McNinja.
 * Happens in Anti-HEROES #67. Kaal is impersonating "Dave" when he runs into the real "Dave", and manages to stay in sync with him for a while before his own stupidity does him in.
 * In Terror Island, one of the main characters tries to sneak into a college reunion under the obviously made-up name "Ned Q. Sorceror, D.D.S.". Turns out the school actually has an alumnus by that name.

Western Animation

 * In the Popeye cartoon Hello, How Am I?, Wimpy impersonates Popeye in hope of getting some hamburgers from Olive, and has an argument with the real Popeye over which of them is genuine.
 * An argument based entirely on Fridge Logic. The only thing that the points brought up in the argument actually proved was that one of the two wasn't Popeye, without providing any evidence as to which one was the real Popeye.
 * Popeye still believes it, and walks off trying to figure out his 'real' identity.
 * In Bizarro's first appearance of Superman: The Animated Series, he looked and acted just like the Man of Steel (except for being really corny). The real Superman was tipped off that something was wrong when Bizarro rescued Clark Kent from falling off a cliff.
 * Parodied in the Family Guy episode "Road to Germany:" "Two priests?! That's impossible!" Later in the same episode it's played straight, complete with Mirror Routine. Also played straight in another episode when Peter tries to impress a high school classmate by claiming he grew up to be "Neptune, God of the Sea" only to find out that the real Neptune is playing at the same miniature golf course and doesn't appreciate Peter sullying his good name.

Real Life

 * There are lots of urban legends about fraudsters trying to pass off fake or stolen IDs that turn out to be relatives of people in the queue behind them, or the manager of the store they're trying to rip off.
 * One variant on this theme (possibly apocryphal) has reports of drivers being stopped and offering false ID—that turns out to belong to the cop stopping them (or a relative/close friend of same).
 * There is a verified case of a forger in California who attempted to pass a forged check written on a checkbook he had stolen from a mailbox. The teller was the actual person who owned the checks.
 * In another real life example, a police officer pulled over a possible drunk driver, who pulled into the driveway of a nearby home and claimed it was his home. The problem? You guessed it, it was the cop's house.
 * Versions of just about all of these have shown up on (The Customer is) Not Always Right.
 * Happens all the time in the party game, Mafia, and its update/remake Werewolf (a game modeling a battle between an informed minority (the mafia) and an uninformed majority (civilians), with some of the latter given special roles to help their cause) Occasionally, a mafia member tries to claim that they are the doctor/detective (the most valuable of the aforementioned special civilians) as a last ditch effort to save themselves from being voted out, knowing full well that the said character will instantly know that they are lying but banking on the fact that there is a good chance of them getting away with it as the said characters can't (or won't) always come out and call their bluff. Sometimes, such a bluff does get called, and another mafia may try to pull a jonesy on the real character, and then good fun is had by all. At least the ones on the mafia side, who know whats going on. Yes, the game is less a 'battle model' and more an exercise in lying/detecting liars.
 * This gets very layered when mafia use this trope to their advantage. A mafia can claim to be a detective, knowing that the real detective can pull this trope, just to find the detective and kill them. If the detective says nothing, however, then the mafia can run the town unopposed.
 * Trading the detective for the mafia isn't necessarily a bad trade-off for the villagers though.
 * When confronted by a situation like this in mafia, the best course of action is often to lynch neither of the people claiming to have a special villager role. The mafia will most likely be forced to kill the (real) detective sooner or later anyway. The biggest mistake the villagers can make is get tricked into believing that they have to make an uninformed decision right that very moment. Killing a wolf now or later usually doesn't matter, as the only dead wolf that matters is the very last one. In the meantime though, a special villager role can still do his thing and help out.
 * Happened in Real Life in a psychological experiment referred to as "The Three Christs of Ypsilanti". A certain psychologist wanted to see what would happen if one's identity was constantly questioned, and put together three patients, all of whom claimed they were Jesus. Hilarity Ensued.
 * This can also happen when something other than a person is disguised. During World War I, the British and Germans both employed armed merchant ships (the Germans used them to attack British shipping, the British to hunt down German raiders), and often used fake markings, false smokestacks, and other elements to disguise them as the other side's ship. In the 1914 Battle of Trindade, the German SMS Cap Trafalgar encountered the British RMS Carmania, both of which were disguised. The problem was that not only was Cap Trafalgar disguised as Carmania, Carmania was also disguised as Cap Trafalgar. At that early point in the war, neither side actually knew which merchant ships the other had converted into auxiliary cruisers, and thus both ships' captains made poor choices of disguise.