I really had to think about this for a while. The best answer is nothing, because you have no control over what other people will do. The suggestion I offer is to shift your focus away from the things you can't do and focus instead on what you can do, namely finding new people to hang around with.
There's a saying about people critical of some trait about you vs people who accept you as you are: "those who care don't matter, and those who matter don't care." It's not always true (parents are an exception since they matter whether they accept who you are or not), but it's a good guide. Try to find better friends and let everyone who's a drag on you fall by the wayside. People who try to bring you down aren't worth your attention, much less your friendship.
It's hard though. Tuning out the haters is damn hard. Good friends make the hardship easier to bear.