My favourite Halloween costume of all time was my friend dressing up as Dr Frank-N-Furter from Rocky Horror Picture Show. Now that was really "scary".
He never lived it down with a lot of people, but I respect him infinitely more for doing such a cool thing at your own expense. I can assure you he isn't really a transexual because he has nothing to hide from me, he just did it for trouts and giggles.