Friend of mine (female) is dressing up with her jeans, western shirt, cowboy hat and shoes all backwards. It's the 'reverse cowgirl' costume. I thought it was hilarious (had to explain it to the wife, though).
A friend of mine went as a flasher once. Beige raincoat, black bow tie. He did wear shorts underneath. But he had a di!do rigged with some strings to stick out when he opened the raincoat. It was hilarious!!