Body odour. I mean, really, have some people never heard of deodorant? Do they never take showers? Blegh.
I know some people at animeconventions don't shower on purpose that weekend. The gameroom smells like a slaughterhouse in midsummer anyway, so why sacrifice those precious ten minutes of their time to pour some water and soap over themselves, right? The girls who spray deodorant every ten minutes but don't actually do anything else are just as bad.
Yoda is a fan of proper hygiene