One of the worst things is playing someone who has a bad cold and they keep blowing their nose on a snot rag and touching the pieces. I remember seeing a video clip of Garry Kasparov doing this.
I'd like 2 c that one! If u can find it, either post it here or post a url.
how you dress (and smell) is very important when playing a tournament....first visual can intimidate your opponent (even if you dont recognize it). Personally I like to see men dressed nicely....classic formal wear...no tie necessary....impecable shoes and matching belt.