I found the scariest Halloween costume while I was browsing around online. I don't recall exactly where it was, but it sure put chills down my spine along the lines of Jason or Freddy Krueger.
A particular individual decided to dress up as Barack Obama. Yes, I know; that in itself is scary enough. But he did it with a specific goal. His plan was to go up and down the streets finding the children who had collected the most amount of candy, and take a large percentage of it. He would then find the children who had collected very little candy, and redistribute it to them, so that everyone's candy collection was more even. Of course, we can figure out what would happen here if this became common practice. Children wouldn't waste their time doing the work going door-to-door to collect candy. They'd simply wait for the taxman to "give them their share."
Each year around this time, I'm reminded of libertarian comedian Tim Slagle's method of using Halloween to teach children about taxes.