A theory someone has that they want no more input on, especially if that input would debunk their theory. Usually formed about a person's sexual orientation, questionable gender, or lifestyle choices.
Tom: Dude, that guy's totally gay.
Ed: What? how can you tell?
Tom: If a guy wears a pink shirt, that means he's gay.
Ed: Well what about...
Tom: Shut up! I was being Theorhetorical.