They aren't necessarily assholes. I've met a few PKers and they're quite nice, actually, some are nicer than the rest of the community. See, I've had random snipers with horrible equipment randomly shoot me without even saying hi or anything, and then again I've had some shoot at me after saying hi if I don't reply, while on the other hand, I've had random well-equipped "professional", fully ego-loaded players say hi to me and ask if everything's O.K.
Killing Farmers and Levelers is hilarious, since most say "wats ur main char?? he better be strong" or "w8 me". Then they come in with an Assassin Cross or Champion and die again, then call you a nab or noob. Then log out and never show themselves again on the same map.