Just remember the area they are in, bring a couple of SB friends and whoop his arse :>
If he likes to zerg and kill people without much skill involved - that is his prerogative. Just wait for them to pick on some other poor bugger and while they are distracted just give one of them a nice PA+CD with AE Mezz.
And every time you see them trying to kill someone, do the same back, and one day they might actually try and play fair (but I wouldn't hold your breath :>). This game isn't fair. Kill everything! Especially archers and casters And little luris :>