We're constantly doing things to each other at work and I have some that will work for April Fools or any other time of the year.
We zip tied the sleeves (at the cuff) of a jacket while it was hanging up. When they went to put on the jacket thier arms got stuck (would go almost through the sleeve but not quite) and couldn't put the jacket on.
One I've personally done and works quite well is unplug something and wrap a thin piece of electrical tape on the prongs of the plug and plug it back in. I did this to a coworker's radio at work. They unplugged it, then plugged it back in (didn't look at prongs) and it still didn't work. Then unplugged it and carried it to another outlet all the while not paying attention to the plug and plugged it into that outlet. In the mean time a bunch of us were laughing while he kept trying different plugs and twisting the knobs on the radio. We finally told him when he was about to throw it away.
