You know i never like the alignment system in D&D, never though it really had any place, outside certain class requierments (ranger,druid,pally) and in some cases magic items (intellegent items). For the most part i just let the players play as they wanted to, if they wanted to be a prick thats cool you pay for your actions in the long run, same as if the were nice guys. As DMs we mainly used the alignment too as a way to force peoples charaters to get along, but lately i havent worried to much about it, if people want to kill each others characters so be, its a rough life why should D&D be any diffrent.