My sister's husband, Sam used to play this game with his brother and he re-introduced it to my sister and I when I was last visiting Australia. Whenever it is explained, it sounds really juvenile and people roll their eyes at it. But once it catches on, people can't get enough and seem to let go of their need to maintain maturity.
The game works like this: One person makes a circle by touching their thumb and fore finger, the rest of the fingers sort of fanned apart. The object of the game is to trick the other person into looking at the circle. If they do, you get to punch them. Apparently it was quite violent between Sam and his brother, but now a good natured gentle punch is all we deliver, more to bring shame upon the person who looked, for looking.
There are a few rules. The circle only counts if you are showing the back of your hand. The palm side does not count. You aren't allowed to stick the circle in a person's face, and you can't put it in a place they were already looking. But something as simple as placing it on your shoulder while they are talking to you is enough as they can't help but look. Other popular methods are to make the circle as you hand them something or put it on a door knob that is about to be grasped and so on. You can get very creative with it. Another rule is that you aren't allowed to say "Look at my knee!" and have it placed there. You could however say "I think I have a bee sting on my knee." which would likely prompt the person to look without being instructed to do so. A punch then ensues.
A couple of great ones achieved via the internets. Any "gets" obtained not in person have their punches put in the "punch bank".
Maybe you're reading this and thinking it sounds dumb, but I promise you, anyone who doesn't have a stick firmly up their ass will eventually find endless enjoyment from this game once they let their guard down. Plus, it's fun to punch people.