What to wear: All-black everything; if you can't get your hands on a skintight suit, some black leggings and a tight black top will suffice. You can pick up a black mask and some cat ears at a costume shop. Finish it off with bright red lipstick.
How to act: Flirty but coy; you're a cat burglar, so bonus points if you can stealthily pickpocket one of your unsuspecting friends throughout the night — before returning it, of course.