When my bf's brother was in Airborne school, there were three marines in his platoon. One day, they were out somewhere and nothing was going. They were all just sitting there with their hats on the ground waiting for the Sgt. Airbornes to come do something. So these three marines decide to pass the time tossing pebbles into people's hats. One guy got really annoyed and finally yelled at the marines, "Why don't you guys do something else, like read a book or something!?" to which one of the marines replied, "I can't! I'm a marine!"