Remember...

You can't fight fire with fire. Usually, if someone's being a bitch, it's because they've got some problems of their own. Never let anyone get to you. Whatever they're teasing you about is one of their insecurities. Say you're being bullied because of your weight, the person who is bullying you (i can almost guarentee) is very insecure about their weight. Just ignore them, but never be mean back because karma is a bitch.