Something Only They Would Say / Comic Books

• Daredevil: in the first appearance of DD's ex-girlfriend Elektra, he reveals his identity when he addresses her by his old nickname for her.
• Ms. Marvel: Beyond the Limit:
  • Done unintentionally in the third issue. When Kamala is confronting the doppelgänger, she mentions that she "could murder ten gyros right now". Nakia remarks that that's definitely their Ms. Marvel, since it's a well-established character trait of hers that she's a Big Eater.
  • In the fourth issue, Kamala convinces Nadia that she's the real Ms. Marvel by reminding her of a specific snack they shared when they were getting Nadia's citizenship paperwork sorted out.
• W.I.T.C.H.: In the original comics, Taranee gets captured and tortured by Elyon and convinced that anything she sees is an illusion. When Will comes to retrieve her, Elyon tries to convince Taranee that rescuing Will is an illusion created by her too. But Will says that she's telling the truth and Taranee can read Will's mind if she wants to verify, and Taranee figures it out because Elyon never knew Taranee could read minds.
• In Nightwing: Year One, Dick confronts Commissioner Gordon for the first time in his new guise as Nightwing. After Gordon prompts him to "say something only the kid would say" to prove his identity, Dick struggles for a bit before declaring "Holy Mistaken Identity!"
• In The Return of Superman, Lois Lane asks one claimant to the name Superman why she should give him the time of day. His answer? "To Kill a Mockingbird," which Lane recognizes as the real Superman's all-time favorite movie. Later on, to remove any shred of doubt in Lois's mind, he whispers to her, "No matter what happens, I will always love you. Always," which was one of the last things he said to her before he died.
• In the Donald Duck story "Kappa! Kappa! Kappa!", Donald's nephews see what looks like an ancient famous samurai show up to save kappa from the villainous tengu. They quickly realize the samurai is just Donald Duck in disguise...after they see him running away in panic in Donald's distinctive way.
• In one early The Flash story, this nearly gets Barry in trouble when, while in costume and conversing with a crime scene investigator, he gives the guy a wink that only Barry (as a police scientist) would give him whenever in agreement about something. Naturally, the other cop starts putting two and two together, but Barry manages to convince him by the end of the story that he and Flash are not the same person.
• During Stephanie Brown's run as Batgirl, at one point Clayface forms into an exact copy of her to try to escape a bank robbery. After the two Batgirls shout the standard "Shoot her!" "No, shoot HER!", one Batgirl turns to the detective and declares, "Shoot me. I'll bleed." Detective Gage promptly shoots the other one because no one else would come up with such a stupid plan.
• My Little Pony: Friendship is Magic:
  • During the "Return of Queen Chrysalis" arc, the Mane 6 are affirmed of the CMCs' identity because of their talk of getting their cutie marks from being fillynapped (cue deadpan "It's them" from Applejack).
  • In issue 65, a disguised Princess Celestia finally convinces Twilight Sparkle of her identity by saying she remembers the first time Twilight cast the "spell of Promethea", and Twilight knows Celestia promised to never tell anypony else about what happened.
• Peter Parker!Spider-Man does this twice in the finale of Superior Spider Man. The first time, he attempts to convince Spider-Man 2099 that he's the real deal and Doc Ock had control of his body. Miguel realizes that it is so stupid it makes sense and buddies up with him. The second time, he goes to confront the Green Goblin, who still thinks it's Octavius controlling Spidey. When the Goblin boasts that once the bombs go off, he'll have nothing left, Peter retorts "Except the dignity of knowing I never carried a man-purse", Gobby realizes He's Back!.
  • In a variant, a later issue has the Avengers see a report about Spider-Man fighting a villain who can manipulate and destroy clothes, so he ends up in only his mask and a web-diaper. While Captain America still isn't sure, Spider-Woman declares this must be Peter, because that kind of nonsense could only happen to him.
  • The following issue has Peter going through numerous scans by the Avengers to make sure he is the real deal until they start talking about the time Octavius had bonded with the Venom symbiote, making sure from Captain America that the symbiote went back to his friend Flash Thompson... then decks Cap for hiding Flash's identity from him. This was Cap's proof Peter was back.
  • And in Dead No More: The Clone Conspiracy, Spidey is pretty blasé about fighting a clone of Dr. Octopus. After all, that's not even the first clone of a dead villain he's faced that day. Even when Octavius calls him "Dr. Parker", he just figures the Jackal told him. Then Ock uses the phrase "the Superior Spider-Man", which only the actual dead Dr. Octopus (or a relatively recent Brain Uploading thereof) would know about.
• In Warlord of Mars, Dejah Thoris' grandfather Tardos Mors is presumed dead after a rebellion in Mars' North Pole and is discovered alive inside a ruin in their own kingdom thousands of miles away from where he died. Any doubts that he is an impostor are quickly dashed when he reminisces about a riding incident that only he and Dejah know about, confirming his identity. This turns out to be a subversion, as this "Tardos" is revealed to be a clone created by a telepathic entity that probed their memories and exploited this trope to gain their trust, while the real Tardos really is dead.
• In an issue of Kurt Busiek's The Avengers, the Avengers were thought to be a group of impostors. Carol Danvers was able to prove they were the real deal by reminding a guard of a casual threat she'd made to him years earlier, something an impostor couldn't possibly have known.
  • In the Original Sin tie-in for The Avengers, the heroes encounter a time traveler who claims to be an adult version of Franklin Richards, the young son of their friends from the Fantastic Four. He proves his identity to Black Widow by mentioning an anecdote from his childhood where she showed him how to make Improvised Weapons out of his toys.
• A micro-issue of Teenage Mutant Ninja Turtles (IDW) follows Donatello through a day in his life—from his routine Flame War with an internet forum poster to his run-in with a petulant genius, Harold Lillja, at a convention. The turtle ninja realizes Harold is the aforementioned flamer when he uses the forumer's pet phrases, like "obstruse". Harold deduces who Donnie is as well, and promptly tries to kill his internet rival.
• One story in Doctor Strange involved Shuma-Gorath creating an illusion of Dormammu, who stated that he was there to reclaim his title as Strange's arch-nemesis from Shuma-Gorath. Strange saw through it right away because he knew that there was absolutely no way that Dormammu would ever admit to being second at anything, even with a being as out of his league as Shuma-Gorath.
• Issue 54 of Marvel Adventures Spider-Man has a Something Only They Would Have Heard variation; Spidey blows his secret identity to Captain Stacy when, after knocking two goons out before he could finish his quip, he remarks that "it's lonely being the smartest guy around", which Captain Stacy said moments before to Peter Parker.
• In Superman: Heroes, set shortly after Clark reveals his secret identity, he's worried Jimmy Olsen might break off their friendship now he knows he's been lying to him. It turns out that Jimmy already knew.
  Jimmy: I used to think there were only two people in the world who called me "Jim." Then I realized it was only one.
• Frequently used in DC's war comics, based on the real-life practice of American soldiers asking each other baseball trivia questions to root out German spies. In Unknown Soldier #205 a G.I. remarks that he can't use the old "Who won the World Series" question because German intelligence knows that one by now — so he asks who Popeye's girlfriend is.
• Rocket (2017): A nearly perfect infiltration of Castor Gnawbarque III's office goes all screwy when a disguised Rocket orders a drink. He asks for a Gargle Blaster, not the preferred brand of the guy he's imitating, while his ex is in the room. She immediately draws a gun and shoots him.
• Immortal Hulk: Villainous version. The Hulk figures out who has gotten into Sasquatch with just two words: "Little. Monster." And then one of the most vicious versions of the Hulk has a Freak Out.