Halloween is an instance of visual rhetoric in that it has very specific, yet unwritten, rules about what each sex should wear. These rules change with age and evolve to become less rigid. When children dress up for hallowen, the boys always wear soldier, cowboy, or superhero costumes. The girls, on the other hand wear little princess dresses and all sorts of "girly" costumes. Children never dress up as the oposite sex.
Adults dress up quite differently. There's two basic costumes, something aproved of and something disaproved. Adults dress up as the oposite sex but only mockingly and to show their disaproval. Men may dress up as women, and viceversa, to show they're fear and disaproval of homosexuality.
Halloween is about showing what you love, or showing what you hate.