Have you played this game?
The Ha Game
Teams competing lay down side by side on the floor. The first person lays their head back of next person's stomach and that person lays back their on the stomach of the next to him and so on. The first person in line is to laugh one HA. The next person in line is to laugh HA HA (two times). The third person is HA HA HA. And so on. Any person that breaks out into a giggle is out of the game and must get up and the hole is filled in. The last one to giggle, wins.
Been doing some research for Field Day and came across it on some website. Last time I played it was about 2 years ago with some friends and I'm pretty sure I haven't laughed that hard in ages. In fact, I think I remember my stomach being sore the next day.