In Alone With Her, when the protagonist, the girl he's secretly spying on/manipulating, and her best friend are having lunch, the best friend asks him if he'd been to a particular fashion district in Seattle (since he claims to be from Seattle). He says yes, and once he's out of the room, the best friend reveals that she made the fashion district up.
Lady: Did you see the ad in the Times? Patrick: Uh, yeah. Lady: There was no ad in the Times.
In Black Mask, one of the Super Soldier villains has infiltrated the police and gotten into the unit led by Li's best friend. Late in the movie, Li's friend begins to notice the suspicious behavior from the infiltrator, and begins casually asking the infiltrator a few questions, like how long he's been on the force (about a year) and which department he was in before transferring into this unit. In response to these answers, Li's friends says that means the guy must have served with Captain Chan and talks about how nice a guy Chan is. When the infiltrator agrees with this he's immediately shot: "Chan died four years ago, and he was a real prick!"
In Captain Marvel (2019), after Nick Fury's boss calls him "Nicholas",note Fury having mentioned earlier that no one ever uses his first name Fury realises he's been replaced by a Skrull. He confirms it by claiming their current situation is "just like our mission in Havana",note which never happened, Fury having also mentioned that he only did missions in cities starting with the letter "B" to which the Skrull agrees. Gets a Call-Back later on when the same Skrull, now an ally and disguised as a Kree guard, uses the same line to let Fury know who he is.
Darkman: The villain comments to the title hero, while the hero is in disguise, that he would hate for his (the person who Darkman is impersonating) wife and kids to miss out on such a "great role model." When Darkman answers that they do look up to him, the villain casually notes that he doesn't have any kids, and nailguns his hand to the wall.
Darkman II: The Return of Durant: Durant (the villain) suspects that Darkman is masquerading as Ivan, and to make sure he makes a comment about not having to leave someone's body behind in Saskatoon. He was refering to an earlier conversation, where he's talking to the woman in question in Ivan's presence and states that they'll be burying her in Saskatchewan.
In Dave, Nice Guy Dave happens to look exactly like President Mitchell and has been hired to briefly stand in for Mitchell so that Mitchell can carry on an affair... except while Dave is subbing for him, Mitchell has a stroke that renders him comatose. Put in an awkward spot, the President's advisors decide to have Mitchell cared for in a secret facility while leaving Dave to fully take the President's place, intending to use Dave as a Puppet King. Eventually the President's wife Ellen notices the changes in her husband and tests him.
Ellen: Reminds me of when you were in the state legislature. Dave: Yeah... me too. Ellen: You weren't in the state legislature. (stands up and offers her hand) Hi, I'm Ellen Mitchell. Who are you?
In Diamonds Are Forever, Mr. Wint and Mr. Kidd pretend to be room service and serve Bond and Tiffany diner. After they serve the drinks, Bond remarks he would have liked to drink a claret. Mr. Wint apologizes and says they ran out, then Bond points out the drink they served was a claret.
This trope shows up in Eraser when Lee Cullen, the witness John Krueger (Arnold) is assigned to protect, gets picked up by an enemy agent posing as John's ally (when John was betrayed and on the run). Remembering John's advice to her to "trust no one" and that John only works alone, Lee then asks the fake agent to perform John's Secret Handshake, before shooting the imposter in the kneecap and running. Cue a bunch of mercenaries showing up and pursuing her.
Eyes Wide Shut: This is how Bill is called out during the orgy sequence. He's asked for the house password in addition to the admittance password, which he says he forgot. Later on, he's told that there was no house password.
In Face/Off, FBI agent Sean Archer infiltrates prison perfectly disguised as his arch-nemesis, Castor Troy, in an attempt to discover the location of a bomb from Castor's brother, Pollux. Ever paranoid, Pollux quizzes Archer on what medication he takes, but Archer is so obsessed with Castor that he is able to answer correctly.
In Godzilla: Final Wars, to prove Daigo is an imposter, Anna presents what is apparently Daigo's dog Clint. "Daigo" cannot guess the dog's name, and eventually, Anna reveals it wasn't Clint at all, but her own dog Candy.
Major Marquis Warren and Bob the Mexican go back-and-forth with each other throughout the first half of The Hateful Eight. Warren takes an instant dislike to Bob and doubts his claim that Minnie is visiting her mother and left Bob in charge while she's gone. Eventually Warren stops pressing the point because Bob manages to correctly respond to the traps that Warren lays out to catch him (The first one being able to identify the type of tobacco Minnie smokes) It turns out that Bob is lying, and had helped kill Minnie before Warren arrived. He was able to dodge Warren's questions because he heard Minnie talk a bit before the rest of the gang killed her, but he still gets shot, because Minnie was notoriously racist towards Mexicans and would not let Bob in if she knew who he really is.
Jurassic Park III: Paul Kirby brags that he has climbed Mount K2. Billy Brennan exposes him by asking if he made base camp at 25,000 or 30,000 feet. Paul says 30,000 feet, unaware the mountain is 28,251 feet tall.
In Live Free or Die Hard, John McClane mentions a police code to Thomas Gabriel's mistress, who is pretending to be a police dispatcher. She says that the police had to dispatch all units in regards to the code. McClane coolly responds, "Dispatch all units for the naked people running around?"
The main villain of The Master of Disguise uses this in one of the final scenes to uncover the identity of the disguised hero, who had given himself away by forgetting to change his shoes.
Devlin: Oh, by the way, your wife called. disguise!Pistachio: Oh. Thanks. Devlin: You're welcome. (turns away, then turns back) YOU'RE NOT MARRIED! (rips off Pistachio's disguise)
Variation in Men in Black: Agent K exposes an alien posting as a Mexican immigrant by saying insulting and threatening things in Spanish, but in a cheery tone of voice, to see if he reacted appropriately.
In Midnight (1939), when Eve poses an an Hungarian royal blood, Georges is onto her and asks if the Budapest subway has been finished yet. She replies that the streets are still torn up. However, as George later reveals, the metro was already finished 50 years ago.
In the Gene Hackman film Narrow Margin, Hackman's character tells a pair of "RCMP officers" that he might have the guys who've been pursuing him and his witness all over a train "on a 374". They agree, which tips him off to their being fake. 374 is "indecent exposure".
In The Negotiator, Chris Sabian is trying to talk down negotiator-turned-hostage-taker Danny Roman. When Roman demands to talk to a confidential informant that can't be located, Sabian reasons that Roman doesn't know the guy either. He substitutes an impostor but is caught when Roman slips in a reference to the impostor's time playing ball for Colorado State and the impostor fails to challenge it despite having Arizona State in his personnel file.
The Naked Gun: Muldoon asks the grocery boy where he hid the knife which he stabbed Jean Dexter with. The boy replies that he buried it. Of course, there was no knife involved in the murder and the killer should have known that.
In The Numbers Station, after finding out that the station's one-way operator has also been compromised, Emerson confirms it by phoning and getting the code-phrase slightly wrong on purpose.
Operator: Hello? Emerson: That wasn't the right password. Operator: What? Emerson: That wasn't the right password. [beat] Operator: Tell me you killed the girl before you figured that out. [Emerson hangs up]
T.K.: That first time we met at the bookstore, did you ever imagine we'd end up in a mess like this? Yulaw: Even if I had known, I still would have done it. T.K.:(turns gun on Yulaw) It wasn't a bookstore.
Clouseau: What is your code name? Dreyfus: I don't have a code name! I never had a code name, lunatic! Clouseau: I understand sir, but you see, only the real Inspector Dreyfus would know he did not have a code name.
In Ronin (1998), Spence is revealed to be a Wannabe Secret Agent when he is asked by Sam what the color of the boathouse at Hereford is (the main British SAS base) and is unable to provide an answer. After a shamed Spence shuffles away, Sam is asked what the color of the boathouse actually is, and he replies, "Hell if I know."
In A Series of Unfortunate Events (2004), Uncle Monty exposes Count Olaf (pretending to be a herpetologist named Stefano) as an impostor by asking him to milk Petunia the snake. "Stefano" starts looking for udders. Unfortunately, while Monty realizes Stefano is an imposter, he doesn't realize that he's Count Olaf, which leads to his death.
In Sonic the Hedgehog (2020), Tom is immediately suspicious when Dr. Robotnik announces that he's from the electrical board, so states that he must know his friend who is also a killer baseball player. Robotnik confirms that he does... and Tom stops him from entering because said friend works for the gas company, and is a frisbee player, also pointing out the electric company usually checks outside the house.
In The Spiderwick Chronicles movie, the main character's father seems to appear and he (the kid) asks his dad what it was he wanted to tell him. He's actually the villain, and the kid finds this out because his father was supposed to tell him they (the parents) were getting a divorce.
Stalag 17: The Mole tips off suspicious cabinmates by mentioning that he was eating dinner when the attack on Pearl Harbor occurred. While it was noon in the Eastern time zone when the attack happened, it was dinnertime in Germany.
In the TV movie Stranded in Space, astronaut Neil Stryker crash lands on a doppelgänger planet that circles the Earth in its orbit, always on the other side of the sun. He is rescued by the people of that planet, who look and sound just like the people of Earth, and placed in a hospital, but the leaders of the planet decide to fool Strykyer into thinking he is on Earth. They are able to monitor his dreams while he sleeps and get information about Earth that way, that they then use to convince him he is on Earth. Stryker becomes skeptical about this after awhile, since although he gets cards and gifts from the people he knows (actually sent by the hospital staff), he never gets to see anybody he knew before the accident. He notices his doctor is named Dr. Revere, so, in order to test him, he asks, "Any relation to Paul Revere?" The doctor carefully answers "no," and then Stryker says, "That's OK. Paul Revere was never much of a ballplayer anyway." Dr. Revere admits he is ignorant about sports figures, but seems to have no idea who Paul Revere was, and this tips Stryker off that he is not in an American hospital, though he only later finds out that he is not even on Earth.
Terminator 2: Judgment Day: The T-800 asks John Connor's foster mother a question about John's dog, but intentionally gives the wrong name to see if she's actually the shapeshifting T-1000, knowing that if is Janelle, she'll give the correct name. "Janelle" doesn't react to his getting the dog's name wrong, thus confirming it's the T-1000. In the extended deleted scene, as the T-1000 leaves the house, it kills the dog and grabs a bloody dog collar, seeing the name on it and realizing that its target knows that it's there and will be avoiding the house.
In There Will Be Blood, Plainview recalls events in his hometown to test whether his half-brother really is who he says he is.
In There's Something About Mary, Pat impersonates an architect, which goes well until he meets Tucker, a fellow architect who immediately starts grilling him about his work. Pat manages to fake his way through it, but eventually we learn that Tucker was also lying, and had spotted Pat as a fellow imposter and was trying to catch him in a lie.