One of my high school friends went to work for ComputerVision, and described a prank he'd played on his group's secretary -- one that backfired a bit.
The state-of-the-art printer in their office was a DEC starwheel printer with a tractor feed. It didn't take him long to discover the control sequences that would send the print carriage to the right margin, back to the left, advance the paper one sheet, and back one sheet.
So he wrote a short program to send the printer into apparent spasms: left, right, left, right, form-feed, reverse form-feed and so on. He put a 5-minute delay at the front, and then launched the program just before going out to lunch.
The printer shenanigans did indeed draw the attention of the secretary, but not in the manner he'd intended.
After the first few iterations, the paper jammed on a form-feed. The frustrated stepper motor trying to send the carriage this way and that got rather hot in a short time, and little wisps of kindling paper aroma started to reach the noses of those still in the office. The astute secretary walked over and shut off power before the wad of paper could ignite.
When my friend returned and learned how his little joke had nearly turned into disaster, he felt more than a bit sheepish. I think he chose not to reveal his guilt, however.