Very childish but great fun and all fully tested………….
Fill your colleagues umbrella with hole punch waste, and watch him or her enjoy an additional shower next time it rains.

Leave a message on their desk to call a certain person and leave a number as usual.
The number you leave is London Zoo, and the name depends on the intelligence of your colleague. Anthony Lope or Allison Gater are good if your chum is pretty bright, but stick to C Lion or Elli Phant if there’s no chance of him or her ever being on Mastermind

Staple one arm of his suit jacket together, just below the elbow area, but obviously not whilst he is wearing it. That would definitely be a joke too far. Also make sure the victim’s suit is not hand made in Savile Row as he may not appreciate the joke as much as viscous-fibre man.

Change their screen saver to the roaming sentence, only make it“GET BACK TO WORK YOU LAZY PERSON ” or similar, or worse. Also works well if you type “WARNING _ FATAL HARD DISK ERROR- DO NOT PRESS ANY KEYS _ CONTACT I.T. DEPARTMENT IMMEDIATELY” and your victim doesn’t know too much about computers.

Get into their computer – word- tools – autocorrect, and change their surname to something very similar by not quite the same. Word will then helpfully automatically change their name to your version as they type it. See how many letters or emails they write until they realise what has happened. Especially good prank if you have someone in your office called Banker or Prosser and you are very brave

Put a pair of knickers in his Jacket top pocket, briefcase, organiser, or laptop case. His wife will find it before he does and will really appreciate the joke, eventually.

If you can get to their mobile phone change the language to a different setting. German is good but Turkish or one which just comes up as unrecognisable symbols would be even better. From experience we have found this prank to be very inconvenient and difficult to remedy, so please make sure that your victim has a very good sense of humour and a high violence threshold.

During a small meeting say you are going to the coffee machine and offer to bring back one for your colleague. Return with two empty cups but pretend that they are full. Walk in slowly pretending to try not to spill them, and say something like “these are a bit full and very hot”. Just as you get near your colleague, pretend to trip up and throw the cups towards them. Please note that this works best with plastic cups; china ones are a problem

If you, like many offices, all have the same mobile pedestals under your desk, and are told to lock them when you are not at your desk, swap yours with your colleague after he goes home.
When he comes back in he will try to unlock it, but without success. When he finally gives up trying, and goes to find the maintenance team, change the drawer units back. Watch his face when the maintenance guy opens the drawer first time.