Fake friends are literally so dumb.

Why are people so mean? some may say because they're insecure, others say it because they're jealous. I think that some people just enjoy making other people cry. so I'm not a mean person. I try not to be. but there's this girl who I'm friends with. she's not the greatest person but I feel like I'm stuck with her. but the other day we were all in the bathroom hanging out during recess. I stood up to leave and she commented on my body. she said "Mel you look weird in leggings, like you have chicken legs," and everyone started laughing. I laughed with them because I didn't know what to do. I spent the next hour crying in the bathroom. I want to leave my friend group because they are all so fake but then I would no friends at all, what should I do?