A TV show in Brazil recently pulled off a pretty mean elevator prank that you can check out online. First they rigged the elevator with hidden cameras, and waited for somone to get in. Once the elevator was moving, they'd cut the lights for a few seconds.
And when they came back on, a little girl in horror movie make-up would be standing next to them, and would start screaming. Then the lights would cut out again, and she'd disappear. The girl got in by crawling through a hidden panel.
(The best reactions are at 1:45, 3:50, and 5:52. But one of the women at 5:05 doesn't seem to fall for it.)
This is the second decent elevator prank we've seen recently. Last month, LG showed off new computer monitors by installing a bunch of them on the floor of an elevator, and making it look like the the floor was dropping away.