Go as your closet! Just wear anything even remotely strange that you own. Bonus points for the weirder the conflagration gets. It worked pretty well for me last night, I wore a black trenchcoat, an American Dr. Suess hat, and a red cape. Easiest costume ever. =P

I'm a sheet ghost this year.

With two extra eye holes, because mistakes.

Do that.

Find a store that's selling Christmas items, buy santa hat. Go as the guy who forgot what holiday it was