The invite screen will tell me that someone I'd like to invite is already playing and already friends with me, but there seems to be no way to figure out *which* friend they are unless their glitch name or "real name" clues me in. I realize that there are privacy issues with revealing that the person I know in-game as J. Glitch is real.name@gmail (or whatever) but at least it could let me send them a note and they could decide whether or not to respond.