Sexy werewolf kills me every time, but sexy ghost is my favorite.
It's just a sheet and sexy legs or lingerie on top of the sheet. It's a great spoof; You don't even need to be hot, skinny, or even female for the costume. It's perfect.
I remember one Halloween party when one of my coworkers went as Eve before she ate the apple. Needless to say we all saw that yes she was a natural blonde