Why do guys do this to their girl FRIENDS?

Maybe it's time to back out of this relationship with the "guys" they obviously are NOT treating you like a "girl" but more like one of the boys. bantering back and forth should not be hurtful or cruel. I don't think they sound like nice guys to me. it seems to me they really think you are too skinny for your height, therefore all the "fat" cow jokes. Stay away from them for a while see what happens. and when and IF one of them asks why you don't come around any more tell the truth that it hurts your feelings to be constantly insulted even in a joking manner.