I've got more work-based pranks(sorry to derail this topic, OP!). Our forklifts are gas powered; that is to say propane canisters that don't have a fuel meter and you've got no warning as to when they'll go flat until they splutter and die. And once they do, you turn the bottle off and swap it out for a new one.
Why do I mention this? Well there's this one guy who hasn't a single funny bone in his body. His job is driving the forklifts all day back and forth, never gets a chance to get off and stretch his legs apart from breaks. At first he loved it but now he can't stand it. So I thought I'd do him a favour and give him a chance to have a little walk.
Once orders are packed, we place them into kingsize black bins. He then comes in at the end of the day, takes these bins on a short drive outside and loads them up.
One day, the boss came over to him and asked him whether a specific item was being loaded or not. The rule at our place is if someone's within 1 meter of your truck you lower the forks and turn off the engine. So while the boss distracts him, I turn the gas off on his bottle. I'm not clocked by the driver, but the boss has seen me as has most of the workforce.
Once the deed was done a few of us went outside - we've turned the gas off a few times on trucks and can guess roughly when they'll cut out - so he fires up his forklift, grabs a bin and drives outside. His truck coughs and dies just where we're gathered, which led to him instantly knowing someone's killed his gas.
Amazingly, he found the funny side of it, especially when the boss was lurking in the background ******* himself.