Well, I'm also the one who knows the most stuff about the game, so you're not wrong. Also, my sense of humor in-character often involves saying ridiculous things half-seriously to see what kinds of responses I get, and just hold my ground on it and find ways to argue in favor of whatever I said. In that sense, I kind of play a character that you know is saying some utter bullcrap sometimes, but is still smart enough that it's hard to point out without his point sounding less like bullcrap when you're done disputing it. The character kind of carries over when we play Mafia, where people are really afraid of me but usually let me by because I never say anything incriminating.
You're kind of a character, but I'm not sure that you're actually playing a character so much as just feeling more comfortable different environments.