For an obscure, retro-pop reference, you could always go as the Unknown Comic.
Whatever happened to that guy, anyway?
Many years ago, there was a bit of a problem with hospitals and companies dumping medical waste into the ocean, and such waste would wash up on shore.
So a friend of mine dressed as a hypodermic needle and was holding a sign that said, "where's the beach?"
In law school, my three close friends and I picked up hockey goalie masks at the sporting goods store. We put on dark clothing, added the masks, then showed up at the official school party. We didn't talk to anyone or each other and we didn't eat or drink anything. We just sat quietly in the back of the room.
Turned out that no one caught on to who we were (we expected to be pegged within minutes) and, over a period of about 90 minutes, people started freaking out. They were about to call the police, when one of my friends took his mask off and lost it. The rest of us did the same. Everyone was a little angry that we let it go that far, but it was worth it.
