Paintball has been a popular game/sport with men and some women since the 1970's. It involves individuals or teams shooting at one another with airguns using paint for ammunition. Gear includes guns and paint, as well as protective gear, and it can be played indoors or out.
Wikipedia estimates that 10 million people in the US play annually. Considering we just hit the 300 million population mark, that means that one out of thirty men, women and children play.
It seems that it was developped by two guys who were inspired by the man-hunts-man short story, The Most Dangerous Game by Richard Connell. It's an excellent read, by the way.
Now, a game for big boys: Tankball. It's like paintball, only, well... from tanks.
Upping the ante a bit, you have to go to Northhamptonshire England to try it. Testosterone junkies have it there, and you can wait until it comes to a field near you, or fly there to try it if you can't wait.