If you want to play a prank on your colleague in the office, a good trick to do it is to frighten him by "spoiling" some of his/her important documents. How to do it? Well, very simple. Under some pretences take important documents (for instance, your chief asked you to bring them, or you want to look at some details, etc). Take them and go away. Go to a Xerox and make copies of some sheets. Return to your colleague, put the pile on the table and exchange a couple of words. At this point you "accidentally" spill your coffee/tea/coca-cola/juice on the documents. Your colleague is shoked! He starts either yelling his head off or simply turning red in the face! But here your take out original documents!!!
However, choose the right victim, with a good sense of humour, coz pranks at work are not always welcomed.
You may also play it on April Fools' Day! Good luck!