Most places I've worked, and relationships I've had, were big on pranks, so....
I stuffed a found dead mouse in the toe part of someone's sneakers they'd taken off.
I stuffed a biology lab rat in someone's potato chip bag. (Every morning she put a big bag in the side drawer of her desk and munched on/off; when it got low enough but not empty, in went the rat.)
I enlisted help in emptying out a boss's office (desk, everything) and shut the door. Boss walked into his office with HIS new boss before we could give him a head's up.
A guy once smeared the underside of my car door handle with chocolate frosting-----we worked in a zoo so your mind instantly went to poop! To get even, I had to orchestrate the event and organize other people to help with the timing, but I hid in a big garbage dumpster (cardboard-only dumpster) waiting for him to slide open the door, where I simultaneously screamed bloody murder and threw cardboard out at him. He FLEW back, screeching like a little girl.
Glued someone's office door shut.
Saturated a co-worker's fabric chair with water; they couldn't see it was wet b/c the fabric was black.
This took two of us, each armed with huge rolls of heavy-duty packing tape in commercial tape dispensers: took our victim by surprise (shock and awe), wound him up in the tape mummy-style, and then taped him to a wall.
Taped a sign to a new part-timer's back, a young, shy teen: "Help me. I'm new and I'm shy. Please say, "Hi, Mike!" (Came a point in time he asked how people knew his name. I said, "Think about it....").
Sent the same kid (alone) up the new tiger trail at dusk the first day the exhibit opened but after the zoo closed, knowing he didn't know about the life-sized tiger model that growled, sensing any motion, that sat on a blind corner of the trail.
Co-workers Gorilla-taped the bottoms of all the telephone receivers in their cradles in both of my departments on a morning they knew I was working alone, and then kept calling. (This is how World Wars begin.)
Replaced someone's milk with buttermilk. (It shot through their nose.)
Geez, the list goes on and on. And on.