The rule is, anytime you get 2 or more bored guys together a game will materialize. Call it pack theory, machismo, or whatever, this is a certifiable rule. But you're probably saying, "Terry, me and my guy friends don't do that." Well congrats, you guys lead an exciting life full of nonstop action or you've already lost your man cards (see married).
So the other day, Sherman and I were sitting around a pool being bored with a cooler full of soda and beer cans. We started talking about submarine movies and then bam: U-571. One man is the submarine and has to swim from end to end while the other guy hucks depth charges (full unopened soda can) at him. You can come up for air at your own risk, the game ends when sub makes it to the other side or gets hit. Bonus points if you knock someone unconscious or refer to your penis as a periscope.