Bob suffers Easy Amnesia while wearing an unusual costume or outfit. When he wakes up and doesn't know who he is, he assumes the costume is what he normally wears and tries to fill in the blanks starting from there.
Subtrope of Identity Amnesia.
- One Batman comic starts with Batman waking up, only remembering who he is on seeing his outfit. He travels through Gotham, and manages to intimidate at least one crook into abandoning his initial plans, but when he tries to stop a larger crime he's quickly beaten down. Then the real Batman shows up, explaining that the man we've been following since the beginning is an ordinary citizen (who likes to get kinky in the bedroom). He and his wife were roleplaying a Rescue Romance scenario when the man hit his head, resulting in the comic's events. Batman leaves, but asks that they stick to Superman outfits from then on.
- Soda: One story has Soda suffer a milder form of amnesia in which he doesn't forget who he is, but what he does: instead of a cop pretending to be a pastor for the sake of his sensitive mother, he acts like an actual pastor, condemning the violence of his fellow cops and being nice to his mother's evil cat.
- In one Jimmy Olsen comic, Jimmy is in disguise while on the job and hits his head. "Luckily", he happens to be carrying false documents that inform him that he is elevator boy Dick Hunter.
- In an issue of Jonah Hex, Jonah borrows a clergyman's clothes to spring an ambush on some outlaws. A rockslide kills the outlaws and the preacher and leaves Jonah with amnesia. Seeing his clerical garb, and finding a letter in his pocket appointing the preacher chaplain of a nearby army fort, Jonah assumed he must be the chaplain.
- Inverted in the story "Danger From The Stars!". Superman tries to stop a meteor with some Kryptonite in it, he gets hit on the head, and falls down to a costume ball. He figures he was just attending the party, finds his civilian clothes in a pocket in his cape, and assumes his glasses are just to prevent eye fatigue. He goes to the Daily Planet, figuring a newspaper would cover an event like the ball, where he learns about his Clark Kent identity and his job, and how Superman was his "friend." He later discovers that he has Superman's powers, and instead of putting two and two together comes to the conclusion that Superman's powers came from his suit and that Superman gave it to him to finish up the meteor job.
- One comic had Lois Lane suffer a blow to the head while dressed as a cowgirl at a dude ranch, and believed she was Annie Oakley thanks to resembling her while in costume.
- An issue of The Simpsons sees Homer suffer amnesia while at a costume party and conclude that he is Radioactive Man based on the costume he was wearing at the time.
Film — Live Action
- In Santa with Muscles, Hulk Hogan pretends he's Santa Claus and gets amnesia while in the suit.
- Downplayed in Memento: Leonard is wearing a formal suit for the majority of the film, which is revealed at the end to be someone else's, which Leonard forgot soon after he donned it due to his anterograde amnesia. When Teddy asks him where he got the suit, Leonard assumes he bought it with insurance money from his wife's death.
- Buffy the Vampire Slayer: In Tabula Rasa, Spike wakes up with amnesia in a stolen suit coat with a note addressed to "Randy" in the pocket. Being Spike (and therefore British), he's furiousnote .
- Somewhat related: Anya is wearing her engagement ring, but assumes that she and Giles are together, since they also find paperwork showing that they co-own the magic shop.
- Star Trek: The Next Generation episode "Conundrum". After an alien ship scans the Enterprise, all of the crew members develop amnesia. Worf assumes that he's the captain because he's wearing his decorated Klingon sash.
- On The Mist, an amnesiac character awakens in the woods in military fatigues, and a wallet with ID for a "Bryan Hunt". He doesn't catch on that this isn't his name until he makes it to the hospital and encounters the real Bryan Hunt, who's being treated for injuries inflicted by someone who beat him up and stole his clothes.
- In the NMS story flashback arc in Sam & Fuzzy, Fuzzy wakes up with Laser-Guided Amnesia and wearing nothing but a bowtie. He assumes, based on his teddy-bear-like appearance, that this is his default state of clothing and keeps on wearing nothing but the bowtie for much of the comic. It's only after discovering an old jacket and talking to Hazel that Fuzzy learns that Eric used to walk around fully clothed. He's quite shocked by the discovery.
- In The Strangerhood, Sam (who, like the rest of the cast, has no idea who he is or why they're suddenly living on the eponymous street) is able to find out his name because it was written on his underwear. In the finale, it turns out that this isn't his real name (and those weren't his pants)!
- In Lilo & Stitch: The Series, one of the experiments afflicts the cast with Laser-Guided Amnesia. Since Gantu has a weapon and his old Galactic Armada uniform, he believes himself to be some kind of police officer instead of the show's resident Anti-Villain.
- In an episode of A Pup Named Scooby-Doo, Shaggy gets amnesia, and since he was wearing a Commander Cool costume at the time, he assumes that the actually is Commander Cool, and that Scooby is his sidekick, Mellow Mutt.