Bullies thrive on the pain they inflict and they feed on the reactions of their victims. There are 3 things you can do to fight back against bullies:
1) Expose Them. While bullies are notorious among small groups they're rarely widely identified. Bring them out into the open.
2) Fight Back. It's the last thing they ever see coming. They choose people as victims because they're easy targets. A bully never goes after someone bigger than themselves and that's only because they don't expect their victims to fight back.
3) Trivialize Them. This is the most important. Remember in the 3rd Harry Potter movie where there was a creature in the closet that turns into whatever you fear the most? And all you had to do to defeat it was turn it into something funny? Bullies can't stand to be trivialized or made fun of. They have to be taken seriously or they cease to exist.
I realize this may not always work in practise but the methods are effective...you just need to find out how to apply them to your situation. There are always ways to fight back.
No one has to be bullied.