I like to wear a costume to work on Halloween. Of course, it's got to be fairly subtle and appropriate. Last year, I wore a suit and small (very small) devil horns, and had a clipboard of infernal offers for interested buyers. This year, I've got a short wig (which a distressing number of people have mistaken for my own hair) and some accessories that are reminiscent of another co-worker's style. His nickname is the same as my name; it seemed funny at the time, but now I'm thinking not so much.
Of course, by 8am I had a better idea. Should've gone with grey top and pants, a grey tail and grey bent-over cat ears. Pin a caption on the shirt and I'm a LOLcat.