Borrow the victim's cell phone when they aren't around and change the language setting to a foreign language. Then watch and laugh as they struggle to translate the setting instructions on their phone.
Are you talented with Photoshop or another photo-editing program? Then work your magic on your victim's desk photos! Borrow their photos, scan them, then: switch out their family members with monkeys, change their appearance so they look fat, photoshop them in embarrassing places, etc. Let your imagination go wild!
Attach a string to the back of the victim's desk drawer. Then run it up the wall, into the suspended ceiling, to a small container attached to the ceiling directly over the victim's head. When the drawer is opened the string will be pulled, dropping a shower of confetti onto the victim's head.
Take an item from the victim's office (something they use a lot such as a special coffee cup, stapler, pencil cup, etc.). Take a picture of the item and leave it on the victim's desk (in the same spot where the item was located), along with a "ransom" note.
Not Silent, Not Deadly
Set the ring tone on your cell phone to an embarrassing bodily function and turn the volume up all the way. Hide your phone in their desk or under their chair. Call your cell phone from your desk phone. Everyone will think your victim has a problem!
Submitted by HK
Trapped in Plain Sight
Take a token item from the victim - place it in a Jello mold, freeze it in a bottle of water, place in the center of a rubber band ball, etc. Keep taking the item and pranking the victim repeatedly.
This Prank Smells
Get a gang of people to help you pull this prank on your victim. Throughout April Fool's day, when each person is around the victim, they should pretend to smell something stinky. Ask the victim if they smell it too. After several people in a row do this (separately), the victim will become paranoid that is is THEM that is stinking.
Submitted by Ulee
Make some copies of a paperclip. Then put them into the paper tray of the copier. People will go nuts trying to find the paperclip stuck in the printer.