High school can be tough. Not only are you going through the very awkward and troubling ritual of growing into your adult body, but you've got a bunch of people surrounding you who are, presumably, just as insecure as you are.
People tend to deal with insecurities in different ways. Some, if raised right, show empathy and try to help others get through their tough times. Others might take a more hurtful approach, like bullying and teasing so they could feel better about themselves.
These people obviously are the worst. That's why it's so awesome when a bully gets their comeuppances.