A person who rudely interrupts a conversation with random drivel about their opinion/personal life that is irrelevant/stupid. Something Theron doesn't do.
Theron: This meteor shower only happens like every eighty years or so.
John: Yeah, this is rather magnificent.
Cockneck: My girlfriend is such a bitch dude!
Theron/John(in unison): Stop being an ass-be-lonker while in our presence.