These days I feel left out of the whole April Fool's Day thing. I'm not much of a prankster, partially because I only have five coworkers and they're even older and crabbier than I am, and partially because I'm a pussy and I hate hurting people's feelings.
Although... it wasn't always this way.
Some ten years back, my coworkers and I got it in our heads that it would be really funny to take a screenshot of the supervisor's computer desktop, set it as his wallpaper, remove all of his desktop icons, and hide all the toolbars. So when he returned from lunch his desktop looked exactly as it did before except nothing was clickable -- it was all just an image.
We sat hunched over at our desks with our fists stuffed in our faces to keep from laughing as we heard him in his cubby, mousing and clicking and swearing. He fancied himself quite the sophisticated computer user and he was too damned stubborn to admit he couldn't figure out what in the hell was wrong.
After about half an hour (and at least two cold reboots) he called for help. We, being the helpful types, exploded into hysterical laughter.
As good as it was, unfortunately that prank is effective only once per office.
The Ex used to tell of an awesome prank from when he was teaching Submarine School* in the Navy, but I can't remember if he actually pulled it or has heard about it.
As the story goes, one guy was very proud of his desk by the window -- the only window in the shared space. His coworkers disassembled his desk and reassembled it exactly as it was, down to the last paper clip and coffee mug, on the rocky ledge right outside his precious window.
Remember that email making the rounds about office cubicle pranks? I found some of them on this site. Check it out -- there are some new ones! Even though I believe my pranking days are behind me, I do love the keyboard and mouse jello molds...
Maybe it's a good thing Evil Twin and I live on opposite coasts now.
* Yes, there is such a thing, I swear.