Okay, this is a simple one from a few years ago. It doesn't take much overhead; If you've got a workshop, you've got all the supplies you need.

If you've got someone at work who needs to be taken down a few pegs, why not fill their desk with sawdust? Come on, you know someone who deserves it. ;)

Step 1: Select Your Victim

Be honest, you've already got someone in mind. If not, keep an ear open for some key phrases like:

"I'm glad no one decided to prank me on April 1st!"
"You've got to go big or go home!"
"I'm a pilot."

Sir... as they say, challenge accepted.

Step 2: Gather Materials

Gather up a few bags of sawdust from your Shop Vac. If you're not completely evil, use a window screen to sift the chips away from the powder. Bag up the chips and heavier material; toss the powder unless you want to really ruin someone's day.

Step 3: Deployment

Head to the target early and pack their desk drawers with the sawdust. And don't you dare take anything out. It's just paper and come on, they deserved it!

Ideally, you'll want to fill each drawer precisely to the brim, making sure every article within is completely hidden. Carefully close the drawers and use a vacuum to remove any evidence.

Step 4: Execute!

If you're able, keep watch for your mark to enter his office. Don't give him enough time to find out for himself; walk by with a notebook and ask for a pencil or something you know he has in the drawer.

Andd..... let them go fishing! If you're nice, leave the vacuum with them. ;)

Step 5: Prepare for Retaliation

Of course, you know that's not going to be the end of it...

Some other options (I'm not making a whole pile of separate entries for these):

-Operation Carpet Fresh: Using a few thousand cups of water and the staff on swing shift, fill an office with full cups of water.

-Sticky notes! If you're asked to take messages while someone is away, don't disappoint them.

-Cubed foam. If you're ever customizing Pelican cases, keep the cubed foam that you pluck out. Barricade your victim's office door, hop the wall and fill with the foam bits. Add more in the drawers.