In a pinch during my sophomore year at college, I devised the most disconcerting Halloween costume I've ever seen. Being lazy and broke, as most college students tend to be, I had only prepared for the holiday's festivities (such as Trick or Drinking) by going to the local costume shop and purchasing the only thing I could afford: a black hood with special black cloth over the front that the wearer can see out of while remaining hidden from others.
I had on hand a tux from being in the University of Illinois Varsity Men's Glee Club. I donned that, along with a black button down shirt, black socks and shoes, black leather gloves, and a black bow tie, as well as the hood. Last year I used the same costume, and added to the ensemble an old rusty scythe that was inexplicably in the attic of the house my roommates and I were renting.
While wearing this costume, no one would talk to me. I made sure to play the part of whatever the heck I was supposed to be, standing very still, not speaking much, and when I did move, I moved with a very determined purpose, walking straight up to whoever I wanted to speak with.
People hated it. Many people asked me to take off the mask because it was so unnerving. For $7.00, I would say it was a pretty good costume. Good at ruining the mood, anyway.