Never been to an anime con, never will. But I can only imagine how bad the smell is.
E3's not like that, but it has its moments.
On a similar note as B.O., bad breath drives me absolutely insane. Back in Vancouver, I often wondered if people on the trains/at school/in the malls etc. had brushed their teeth or ever heard of gum. It's gross. (And I hate to say it, but it was far more prevalent among Asians there...) I get paranoid about my breath, especially after coffee, onions, garlic etc. so I always have some kind of gum.