The whole pranking drive-thru employees thing has been around a while, and it's basically just annoying at this point. But here's one that's actually pretty funny.
Some guy made a costume that looked like the front seat of his car, so that when he got in and drove around, it looked like the car was driving itself. Then he went through a bunch of McDonald's drive thrus and freaked out the employees.
(--Search for "Drive Thru Invisible Driver Prank." He goes to the first drive-thru window at :38. And don’t miss the guy at 2:35 who keeps turning away, then turning back to see if his eyes are playing tricks on him.)