some observations...
ugly dudes can get action all night if they have a nice costume.
average chicks can look super hot in the right costume.
it's very easy to talk to anyone - costume is ideal icebreaker
everyone is horny, most of them drunk.
for single ppl, it has to be the easiest day of the year to hook up. hordes of half-dressed girls with an excuse to dress slutty, and anyone with flaws can hide them with the costume.