People who officially remove themselves from the "potential friend" category AND aren't "authority figures" stop mattering to me--I care about them as people, but since they've got no effect on my life and they're mean to me, I quit trying to use social skills on them. Basically, I stop censoring myself (except for anything illegal, which I still would censor). I don't actively try to do mean things to them, but when I talk to them (if at all) I do it for my own enjoyment. I don't "back off" if I'm talking about their "personal" things; I don't "leave them alone" just because they want to; I don't help them with anything unless I'm feeling particularly nice that day. I talk AT them, not to them. I don't even stop myself from saying things that might hurt their feelings.