It's human nature, if you get treated like shit by your boss, you will get your own back somehow. You'll steal as much from him as you can get out the door, or you'll sabotage your equipment for the next person who'll take your job. Open the computer up to worm viruses, take out or unplug hard drives.

Leave graffiti on the walls, stick rotting food or dogshit into the AC ducting or above the false ceiling. Clog up the toilets, pull up the ball cocks in the toilets so they gradually overflow.

I was instructed to lay off some employees at Christmas once by a miserly boss to save his paying them holiday pay, and those are some of the examples they gave me as to what would happen. Guess what, our stores were broken into soon after and emptied of anything that could be sold and even with extensive security guards and cameras etc. nothing was seen.