Also, depending on the model of the copier, it will not let you copy money, and if you attempt it too many times, it will literally brick the machine.
Something cool to do is to take your phone and turn on the selfie camera. Lay that on the platen and make a copy to see a trippy pattern.
If you want to screw with someone, lay a single paperclip on the platen and make a bunch of copies of it. Take your copies and shuffle them into the paper tray face up (assuming you’re using an office laser copier) so every once in a while, someone will get a paper clip on their print.