They can't fault your costumes, so they attack your looks. It's just how jerks are. Be flattered - you have no say in your appearance, but your costumes are YOUR work, and that's something to be proud of, right?
I get a lot of nasty comments about my face, and I think... it's not me they're insulting, it's my parents! And they don't seem too upset about having an ugly daughter... XD Hahaha, maybe it's not the right attitude, but it means I'm not crying myself to sleep about some idiot's remark to impress their idiot friends. Always find the good in the bad!
Please please please don't publicly react - that's what they want. If they know they can hurt you, they'll keep doing it. Never let your enemies see you bleed.