Hosting a costume competition is a pretty common event idea, especially around Halloween, but some folks either don't have the time or lack the enthusiasm for putting together an entire costume. Holding a decorated hat competition instead opens the playing field to anyone who can wield a tube of glue. This is a good one for work because the hats can come off easily when business visitors arrive. Charge a flat fee to participate, and hold a formal hat judging with prizes. If there'll be a large group involved, include lots of categories like the silliest hat, tallest hat, and most romantic hat -- you know, camp it up. Have a hat parade through the office, and display the winning hats in the break room or conference room for a couple of days so everyone can see them close up.