chinstroker
Somebody who stands in a pose at the sides or back of a gig or party, stroking their chin in a misguided attempt to appear being disaffectedly engaged in and/or disapproving of the music currently being played.
Don't bother trying to get across to the bar over there, that entire corner of the room is infested with chinstrokers
chinstroke
One who includes him or herself in on other people's jokes or conversations without being invited to do so.
Mike, you're not in this conversation; beat it ya chinstroke.