Does anyone have any advice...(slander? I really don't know...)?

Personally, I would be honouered to wear something a Sweeney wore. That is the highest honour EVER. But seriously, don't listen to them. He obviously doesn't see it as anything ual, and honestly, I don't either. It's just a pair of pants. They re-use costumes all the time. If those picking on you are in the play, just tell them that they're probably wearing the clothes of some sweaty old guy, if it bothers you that much. Or you could joke with them, if feel comfortable doing that. And, if it comes to it, you could seclude yourself. Hide away in a corner when you're not onstage. That way, you can't hear them. But the best way to deal with it is to sty confident and ignore them.