Obviously friends shouldn't go out of their way to make other friends feel bad, and I have to say that these girls sound more like jerks than real friends. If they think it's funny to make rude comments about you, they're just not very nice. You need to tell them point-blank that the next time it happens, you will consider your friendship over. You should find nice girls to be friends with -- ones who will support you and stick up for you, not ones who make you feel bad about yourself.