The most annoying IMO is the guy in the room who really is smart, but is not (yet) wise. I've run into this with young-20-something programmers who really are

The most annoying IMO is the guy in the room who really is smart, but is not (yet) wise. I've run into this with young-20-something programmers who really are exceptionally bright but lack the perspective of real world experience. These people can be insufferable when they are sure they are right and think everyone who is trying to temper their cocksureness is just being negative.