Gender Vocabulary Slip
Splendid!! Your disguise is so flawless that you are even more beautiful than the average woman, so much so that you become a Chick Magnet (to girls AND boys), and so refined in manner they would never suspect you were ever a man, right?
Unfortunately, being a Hot-Blooded young male all your life has habitually hard-wired your vocabulary to use the masculine pronoun of "Ore" to refer to yourself, something that an everyday girl (who uses watashi, the polite gender-neutral pronoun) or even an upbeat and immature Genki Girl (who uses atashi, the informal-feminine pronoun, or if extreme boku, a boyish one) would never be caught dead doing.
Cue a hurried and panicked attempt to correct yourself mid-sentence, which thanks to the Rule of Funny, almost always keeps the cover from being blown.
Note this is not so much a problem with female characters disguising themselves as boys, as it is not grammatically incorrect for a male to refer to himself as "watashi", though amongst his peers he would be considered unmasculine or excessively polite for doing so.
A grammatical plot complication most commonly found in Japanese Anime gender bending comedies, and occasionally works produced in countries that have gender-specific pronouns or adjectives in their languages (as well as verbs that betray the speaker's gender in first person singular).
There are counterparts in other languages; to say "thanks" em português, one claims to be "obligated" (f. obrigada, m. obrigado), for instance.
If you're speaking about another person, that's Pronoun Trouble.
- Amawa Hibiki of I My Me! Strawberry Eggs almost accidentally breaks his cover on the first day of his teaching job, in front of the whole school through this trope. Rather clunkily translated in the dub with "As a man... uh I mean as a woman."
- Natsuru Senou of Kämpfer falls into this trope so many times it's a wonder Kaede Sakura, the only girl who does not know his (identically-named, at that) female persona and him are one and the same, hasn't caught on yet. Except she did.
- Shiratori Ryuushi, Dogged Nice Guy and The Chew Toy of Mahoraba, was dressed up (against his will and while asleep) to look like a very cute and beautiful blonde. When confronted with Chiyuri, one of his landlady's five personalities who does not know him, he accidentally uses "boku" (polite masculine pronoun) to refer to himself. Subverted in that Chiyuri finds this contrast quite Moe, and that although unusual for a girl, "boku" is used by the nicer-tomboys out there as a pronoun.
- Kuranosuke from Kuragehime is an interesting case. Unlike most crossdressers he does not do it out of necessity but because he enjoys it. His knowledge of female clothing is extraordinary, his fashion sense is spot on and he often struts his stuff in public. Still, very often he slips into using 'Ore', much to to the horror of Tsukimi who is terrified lest her anti-male otaku friends find out his true gender.
- Happens to Psy in an episode of Heroman, when Holly forces him and Joey into crossdressing as a disguise. Though, considering these are American teenagers in the middle of California that we're talking about here, there's probably some kind of Translation Convention at work.
- In Ah! My Goddess, When Keiichi was temporarily caught in a Gender Bender by Skuld's pudding, he tried to play himself off as being somebody else when his sister and friends came around looking for him (for the sake of protecting The Masquerade of the presence of goddesses in his home). He was doing well until he referred to himself with the masculine 'ore' pronoun, rousing suspicion in his guests.
- In Girl Got Game, Sweet Polly Oliver Kyo accidentally uses "atashi" once early on, but immediately corrects herself and uses "boku" consistently from then on. Later, Yura says that she should be using "atashi" since she's a girl . . . then claims he was joking.
- The first known instance of this trope is in a Lord Peter Wimsey short story of the 1930's. Lord Peter watches a sexy French girl berating a man. In French, naturally. He's smart enough to figure out that she is really a man in drag who turns out to be a notorious jewel thief.
- Highlander had this in the ep 'Bless The Child'. A woman had stolen a baby and was claiming it was hers after her own child died. Duncan caught her slipping up, though, and using the wrong Lakota word when speaking to the baby. The baby was a girl, but her own baby was a boy, and she was used to using the word for 'boy' and not 'girl' and hence mixed them up.
- In Breath of Fire 2, one possible tenant for your town is a guard who stutters when he says "ore." He's not only a woman, as it turns out, but the princess of Highland in disguise.
- Referenced to in Wandering Son. The two Transsexualism protagonists, the female-to-male Yoshino Takasuki and the male-to-female Shuichi Nitori, had a conversation about this. Nitori still uses "boku", despite being very feminine and even when dressed as a girl, and Takasuki uses the gender neutral but socially feminine (or formal) "watashi". They both decide the pronouns fit them, so they'll keep on using them.