Exploding Golf Ball
A golf ball that explodes into a blast of white powder on impact - a great gag to slip past your golf buddies (and on the cheap, too).
On close inspection, this golf ball looks just a little bit different than a normal golf ball. There's no writing/logo on and the dimples are a little bit deeper than a regular golf ball. If you put this in a friends golf bag, he just might notice it.
However, you could disguise it by teeing it up for him or doing a quick swap of golf balls on the course. Maybe you just tell him it's a high end, super quality golf ball and he has to try it. Then make sure to tell some people to watch and get a video of it for Facebook :)
The explosion is pretty cool - it seems like talcum powder. And while the powder will wash away in the rain, the remnants of the exploded golf ball will not. If you want to keep the course clean and not piss people off, you'll have to pick up the little shards.
Just make sure you don't have anyone who is a super stickler for the rules in your party, otherwise you might end up with a two stroke penalty. :-p
See it in action here: