Tape a bunch of condoms and altoids (or the breath mint of your choice) all over your body... You are a "condom-mint" like ketchup... get it? Not many people will but you will get the added bonus of having stangers talk to you all night about your costume, and then get to watch them feel stupid for not getting it...
Or cut out a cardboard circle (an old pizza box lid will even work) and stick and alarm clock, and half burt candle, a couple of condoms to it and then drap a bra or pair of boxers over your shoulder... when people ask tell them you are a "One Night Stand"...