Amnesiac Costume Identity

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.

Examples:

Comic Books
  • One Batman comic starts with Batman waking up, only remembering who he is on seeing his outfit. He tries to stop a crime and is 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 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.

Film — Live Action
  • In Santa with Muscles, Hulk Hogan pretends he's Santa Claus and gets amnesia while in the suit.

Live-Action TV
  • 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, he immediately complains about the vulgarity of said name in British slang, but it sticks.
  • The Twilight Zone episode "Where is Everybody?". A man finds himself walking along a road wearing a green jumpsuit, with no idea who he is. When he later sees a movie poster with a U.S. Air Force crewman wearing a similar suit, he realizes that he's in the Air Force.
  • 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.

Web Original
  • 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)!

Western Animation
http://tvtropes.org/pmwiki/pmwiki.php/Main/AmnesiacCostumeIdentity