I'm on a PvP server, but I don't normally mess with people unless I see a fresh Horde corpse and a living Alliance. I'll usually take 'em out, although I rarely camp people unless they just piss me off. Or, like the retard 80 hunter that attacked my lowbies the other day and didn't see the 80 DK in my crowd, I camped him for a bit until he left. Also, I do have a KOS list that spans my entire list of characters, so if you're on that, you're usually incinerated.

Edit: If I'm drunk, which happens a lot late at night on the weekends, I'm usually number 4.