Take a screenshot of their desktop. Set that as the background image. Right-click the desktop and uncheck View -> Display icons on desktop.

Tell them you're going to prank them, and then don't.

Here's one I witnessed in an office about 25 years ago. Some engineers filled a plastic 35mm film canister with a bunch of the waste paper from a three-hole punch. That's basically the little white circles of paper. Then they took a can of compressed air and, with the cap mostly on the canister, slowly filled the canister with super-cooled air from the compressed air canister. Then they fully sealed the cap and went to talk to the mark. They placed the canister nearby -- on the mark's desktop computer, I think. Just out of sight. To avoid arousing suspicion, they stayed and talked to him for 30 seconds or so. Then they walked off to go back to work (and watch the prank unfold from a distance).

That little canister sat there for a while, with the super-cooled air slowly warming to room temperature. As you know, the molecules of cold gasses are very close together, and they start to expand outward as they warm. So when this canister got warm enough, there was enough pressure inside to pop the lid off and distribute the little white paper circles in a perfectly random pattern in a circle about six feet around the mark.

It was glorious.

Ctrl + Alt + up arrow key sets the monitor output to be upside down.

I also am a fan of making the cursor huge and turning on pointer trails.

• Screenshot their desktop
• hide all icons
• set screenshot as desktop background
• watch them die inside as nothing works, not even a restart.

Optional step:

• put your wireless mouse receiver in their computer and subtly click occasionally, or move when they move. Has to be subtle enough for them to question their sanity for a few hours.

I managed to do the above once. Worth it.

If you are close you can plug in a second wireless mouse and mess with it occasionally.

If they don't lock their screen, the old take a screen shot of the desktop and make it the background is good.

DON'T do what I've done a couple of weeks ago - landed me my first HR meeting ever :D

I had to use my coworkers (lady around 50, not too clever with the computers) computer on remote desktop. As I was about to close it, I thought to myself "Perfect setup for a joke". On her computer, I went to https://pranx.com/hacker/ and put in on full screen. Literally like 30s later, our IT guy (he's in the same room as me) get a phone call and all I can hear is shouting in the earpiece. I say to him don't worry, I know what's this about, I'm going to sort it out. I went downstairs and boss's wife is running past shouting that we need to phone the police, I walk into the lady's room and she's hysteric. I say cool down, it's a joke.

Safe to say, they were not laughing (probably the fact that I still was, wasn't helping my case :D)

A very French joke: We used to use their email client and send to the whole team "Hey, I feel generous so tomorrow morning I will bring croissants for everyone. Look forward to it!"

The person would get plenty of "thank you" emails in reply and discover the trick. It was a small office so usually the person would bring the pastries. Yum!

An old boss of mine would find people who left their computer logged in and would send an email to the department from it saying "I love you all so much!"

I worked in a different office and didn't realize that's what was happening. I just thought the Russian guy was happy to be in America.

If you have fixed desks, put a piece of sticky note over the laser on their mouse. That or use the monitor settings to rotate their screen 180 degrees when they aren't around.

Stapler in jello always gets laughs.

Small post it note over the sensor under the mouse.

I've always wanted to try this:

https://live.staticflickr.com/1471/26466314915_efe3f4349d_z.jpg

1. Wait until you have to fart while coworker is away from desk.
2. Position sphincter directly above the tube in the office chair.
3. Lower chair as far as it will go.
4. Fart as you raise the chair as high as it will go, sucking the gassy shit particles into the tube.
5. Walk away.
6. Watch the carnage when coworker sits and lowers the chair.

Put some tape over the optical sensor on their mouse. Bonus points if you print out a little dickbutt picture or something.

Here's one I started planning but never got around to actually pulling off. My team had recently moved from Windows to Mac, had a habit of leaving for lunch at the same time and for some reason never, ever locked their screens.

The prank would go like this: I'd grab a copy of a classic Mac emulator, a System 7 disk image and copies of all the Adobe apps circa 1980-whatever, so that they would come back from lunch one day to find all their beefy new Macbook Pros "downgraded" to looking like this, complete with working Photoshop, Illustrator, etc.

I deeply regret not doing this.

You could 'upgrade' them to a better operating system: https://malisipi.github.io/ubuntu-tour/

🙃

I work at an office which uses Macs. If you have terminal access to a coworker's machine, you can enter say "I'm watching you" and their computer will speak the text. Had a lot of fun with that until they figured out it was me.

Connect a 2nd wireless mouse keep it at your desk let the fun begin

Buy a live lobster, cut the rubber bands off, and hide in their lunch bag.

Pen island dot com

Have any other monitors available?

If you do, literally change the monitor and hide the other one. Smaller the better.