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.
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