My con experiences aren't that bad, but man have I met some freaks. Once, back in 1995, I decided to run a D&D campaign at a local game store. Some wonderful people showed up for my first session, and I made some lifelong friendships that day. But I also had these two homeless bums show up for my game. They stank, their clothes were filthy, they had big gnarly beards, and I think they slept in an '82 Toyota Celica. Jose and Hack. I'll never forget these two gents. I finally worked up the nerve to kick them out of my game after about three sessions. I don't discriminate based on wealth - lord knows I'm not rich - but I'm sorry, I DO discriminate if your personal hygene bothers everyone else at the table.
What sort of characters did they play, you might ask? Cinnamon Stardust and Angelica Moonwhysper, lesbian elven bard and cleric, respectively. *shudder*
Never again will I run an open-to-the-public game. Never.