LARPers - not all that hard to find, even D&D ones have been getting underfoot for a couple of decades at least.
eta - There are some that go whole-hog with top-of-the-line AirSoft stuff (The kind that with all the upgrades cost as much as real EBRs) and go at it high-speed like big-time paintballers, run into those guys and you'll think you've encountered the richest SWAT team in America. Total gear junkies.