Bullies are a part of life, sad as that seems. However, you may notice something about bullies. They can only dish out what they do. If someone pushes back, then they run scared.
They always target soft targets that are too passive to push back. It's really sad when you think about it but it's true. These bullies who go after you, go after those who can't fight back or aren't in a position to fight back.
You shouldn't let anyone push you around. Make sure to firmly make them back off. I wouldn't recommend beating up the bully(although that would get them to back off certainly) but a firm stance will cause them to back off.
Bullying should be considered a crime. Period.