You need to stand up for yourself. I know it's really hard! Believe me, cuz I was bullied once. It was awful and wrong and you don't deserve that treatment. It really brought down my confidence. You need them to stop, so just say,
Bully: Your hair looks like fried potato skins
You: Can you dig a hole and crawl in it?
Works even BETTER than a charm! (At least for me) Oh, and your hair prob does not look like fried potato skins!