Here are some I have used in past year:

I wore complete chef's outfit with a devil's mask and fork. I was (and am) a hell of a good cook.

The next year I put on Western boots and cowboy hat and a black shirt with stars and planets spray glued to it. "Some people call me a Space Cowboy..." - I thought about going as the Gangster of Love the following year but didn't.

I tried the next year to go as something really scary. I was very well dressed but had a small venetian blind hung around my neck with a page from a calendar (one Friday was circled with a magic marker) glued to the slats (sliced at the openings so that the blinds looked proper). Give up? I was a blind date.

Another year I wore a "sandwich" sign which featured a huge "F" on one side and an equally large "G" on the other. I had a hangman's noose around my neck. I was hung in effigy.