Um, he's bored.
He's trying to get your goat.
He's just joshing (Sorry Jonathan)
He's in Halloween costume early.
He thinks you take yourself too seriously (Oops, I think that)
He's a W C Fields fan.
He's got his fingers on the wrong spot on the QWERTY keyboard.
His brain has been taken over by aliens.
If you're still reading this list, what does it really matter?