I kill everybody at least once. Newbie or not. If the guy is completely green, then I won't actively hunt him from that point forward. But if I'm just walking around and happen across him, and it would be counter to my role to not at least attack him, then I'll go ahead and jump him. Though, I might try to do something like spam damage instead of lag, so that he at least has the option of fleeing and quaffing.