Making fun of one's appearance

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I love parties. I usually go to the parties with my friends some of whom are not so close. They have this nasty habit of making fun of people's appearances in the parties. Whether they know those people or not they will flatly comment about their hair-dos, shoes or dresses or anything that might not be appropriate according to their tastes. I feel very uncomfortable in such situations. I have sometimes left parties midway because of their remarks and have never gone back. Please tell me how I should handle these 'friends' of mine? I don't want to lose them. They are not so bad at heart but this quality of their's simply is distasteful to me. Thanks in advance.