Sit down with some friends. Designate a small object, like a notecard or wallet, the prize. Maybe wear nametags. Have a board game in the room. You should play for the prize. I recommend poker, go fish, monopoly, anything like that.
The most important real rule is: don’t touch each other and have fun.
The first real rule is: whoever leaves the room with the prize wins the game. Anyone who’s still ‘alive’ doesn’t lose. Anyone ‘dead’ loses.
The second real rule is: if you make a gun-shape with your hand, it’s a gun, and saying ‘bang, [NAME]’ means you’ve fired it at NAME. NAME is dead, and should either fall over or leave (their choice). If they have the prize, they must put it down before leaving. Once you fire a gun, you must loudly and slowly count to three before you can fire again.
These are the only rules.
You may want to iterate this. For scoring, give five points for the prize and one point for surviving a round. Then start over.
Variants: Use nerf guns or foam boffers for weapons. Have more than one prize. Have all the monopoly money be prizes weighted by value.