There was a friend of a friend who made a whole rant about her hating girls who do skimpy cosplays. Her reasoning was that them looking good makes other people feel bad about their bodies while she went on to call them such vile names that I can't repeat. I called her out on her hypocrisy, jealously issues, and slut-shaming. She refused to speak further and blamed all her behavior on me.
I have recently had some drama with con people but it wasn't related to cosplay. It was because people don't know how to behave.