[AROWHED]

Not technically a prank, but....
I worked in a huge lumberyard Summer of 1989. Another guy working there would disappear for a hour or two during his Saturday 8 hour shift. One day I watched him slip into the pole barn where there was large bags of cellulose insulation stacked about 7-8 feet high, 40 across and at least 30 feet deep to the back wall. Sure enough, he didn't come out for over an hour. Went in there and discovered he had hollowed himself out a hole in that stack where no one could see, along the back wall. He laid down thin boards to walk on top of the stack of bags to get to his hidey hole, and he'd snooze on a small pile of those bags, like huge pillows at the bottom of his hole, while the rest of us were still working and had no idea where he was.
I told another guy there about it, so we got in there and dug out a second hole along his path, then used furring strips to support a single top layer of bags, and left one layer of bags on the concrete floor to somewhat break his fall...effectively creating a tiger trap.
Next Saturday we kept an eye on him, and saw him finally sneaking off into the pole barn....and came limping right back out about 5 minutes later, with a pissed off look on his face. He never said a word about it to anybody...he well knew he'd been caught. Later we went in there, and as we expected to find, the trap was most definitely sprung.