Okay, so lets get this started.
Having been in the military for almost have my life I have developed what some may called sick humor. There wasn't hardly a day went by in the military that some little prank was being planned. It kept the general feelings and thoughts off what was normally a very serious job.
So naturally that kind of humor always takes people by surprise, like making people believe you are going to get them good, but by the end of the day nothing happened. This always works well with someone in authority, I wouldn't pick the person in charge, but I would make them part of the prank. It's called covering your, well you know.
Worked at a small newpaper after retiring from military and government service and one year got together will everyone, pick out the victim and set things in motion. Now this all works because basically people really aren't all that amart as they think they are. It starts with small conversations about April 1st but when the victim comes around the conversation ends quickly. You make sure this happens a lot.
Then you have people start bringing bags of stuff and boxes in. There is always a conference room to put them in. Your victim starts getting suspicous. More conversations and hints about what might be happening in front of the victim, but the victim is not part of the conversation. Now you get the boss to keep the victim busy, the victim feels cut off from what might be going on.
Now it's the first, and to make this work you get some folks to stage some pranks, making sure the victim can see and hear what's going on. Then the fun starts, you call them on the phone/intercom to ask a question and watch how they carefully pick it up, looking for anything. Someone brings them a cup of coffee, they aren't sure if they should drink it or not. They start opening doors slowly, opening their desk drawers slowly. There are some things that you can do to keep the poor victim hanging, but I think you get the picture. By the end of the day they are just worn out, more then if they actually did a lot of work.
So it's go home time and you finally let the poor victim off the hook, so they think, and tell them of the prank. All is well and everyone has a good laugh. The victim leaves and attempts to get into their car, of course you got hold of his keys and made a few changes.