You know the guy in your office that talks too much? The one who can't resist butting in on any conversation within earshot? The one who sees you standing in the doorway of the manager's office chatting, and strolls over so he won't be left out? Yeah, that one. I have one of those, too. We couldn't decide what to call that condition, until Wikipedia helped me out (actually, Wikipedia pointed me to Wiktionary).
Gobshite. Heh. Perfect.