This is a fairly harmless prank that requires a bit of trickery involving a car, a bunch of golf balls, and perhaps some luck.

Requirements:

• Time (medium) - you'll be filling up a car full of golf balls, which could definitely take some time.
• Cost (medium) - you'll need to buy some golf balls. Did I say some? I meant a lot. I've included a link to the right to the cheapest and biggest pack I could find at Amazon.
• Risk (low) - I'm tempted to make this a medium risk prank since it does deal with a bunch of golf balls that will spill out everywhere, but as long as you're good and clean it up you should be fine.

Steps:

1. Buy up a bunch of golf balls, you'll need a few hundred most likely. Follow the link top right to get some cheap 144 packs from Amazon.
2. Somehow get your victim's car keys. Either snatch them without them noticing if they leave them on their desk or somewhere else in the open, or somehow ask them if you can borrow their car to go run an errand saying your car is in the shop for a few hours.
3. Fill up as much of your victim's car as possible with golf balls. The best way is to try and fill up as much as you can, but try and make it so your victim won't notice it before opening the door.

Result:

If your victim doesn't notice that golf balls before opening the door, you'll have a hilarious scene as dozens of golf balls pour out onto the ground. If you want to see what this might look like, check out this funny video commercial that shows just that.

If your victim does notice the golf balls before opening the door, you should still get a good reaction. Also, you'll get to see how your victim deals with trying to open the door without having too many golf balls fall out.

Either way, you should have a fun prank that results in having a bunch of golf balls to take to the driving range to blow off some steam after work.

If you're looking for some golf related gifts (perhaps to smooth things over with the victim of this prank), check out these Golf Goodies.