The feeling you get when you are deep in a conversation, usually gossip related, and someone stops short of revealing a secret they've been building up to for at least five minutes.
So called, because the process is somewhat similar to the way in which one is forced to endure blue balls. While with blue balls, a girl won't finish you off sexually, in blue brains the victim has yet to have their curiosity "finished off." While blue balls is more painful, blue brains is often endured for longer periods of time and cannot be remidied on one's own.
Guy 1: Yo, you know what I heard about Lisa?
Guy 2: No, tell me.
Guy 1: Well, I really shouldn't say...
Guy 2: Come on you have to tell me!
Guy 1: I can't, I promised I wouldn't say anything.
Guy 2: Dude we've been talking about this for ages. Total blue brains.