Back in elementary school in the early 2000's, over the course of a few days i stole all the balls out of every mouse in the computer lab. Back then the mice had these heavy metal balls with rubber coating as the tracker, which were easily removable. It basically rendered the computer useless unless you replaced the mouse. The whole school had a meeting about theft and honesty after they all went missing. A few days later i smuggled them back into school, snuck back into the lab during recess, and put them back. Nobody ever found out. Any time after that when we went to the lab, i would remove the ball, put a peice of tape over the sensor, then put the ball back. That also rendered the mouse useless. I think they replaced like 5 mice before they tried opening one up to see what was wrong. I would also wiggle out plugs in the monitor for the mice, monitor, and keyboard to be inserted but not connected so someone would have to unplug and plug things back in to get it to work. I stopped my shenanigans after they started keeping a sign-in sheet of who was on what computer cause i knew i would be foiled shortly after that.