I just saw a pod on current.tv documenting StreetWars---a 3-week long 24/7 water gun assassination tournament. All participants start with a photo and contact details of their target. If you "kill" your target before getting killed, you then inherit your victim's current target. Rinse and repeat until there is only one left. It's Highlander meets first-person shooting video game meets super-soakers meets awesome. Here are some videos.
I gotta get in on one of these tournaments.
CNN has a video on the phenomenon (sorry, only tested in Windows Media Player)