I work at a community college. A lot of the staff that deals directly with the students (I don't) dress up and really get into the spirit.
The most unusual costume I saw so far was a woman dressed up as the swine flu. Pig snout, pig ears on a headband, white tights, long white t-shirt with two rows of baby bottle nipples glued on and plumped up underneath with fiber fill. Fluffy wings on her back (as in swine "flew", I guess).
I thought it was cute and would be pretty easy to do.
Health is the thing that makes you feel like now is the best time of the year--Franklin Pierce Adams