Geek pranks are nasty and here are a few simple ones:
1. Old is gold ‘Disappearing Desktop’: This ones is tried and tested, though many know abou this one, its still good for many. Here is how we go about it; minimize all windows on the desktop and ht ‘Print Screen – PrtScn’. Now save this desktop image (maybe after pasting it in paint) and set it as the desktop background. Now hide all desktop icons (put them in some folder) and watch the unsuspecting user trying to click non existent icons. A good variation is to leave open a Notepad file on the right end of the desktop before taking the screenshot. This will make the person go crazy trying to close a non existent notepad.
2. Extra mouse: So planning to be a little naughty @ your office? You can really make life hell for your co-workers. Just plug a second USB mouse to your co-workers system and pull it at your end. Now ocassionally control his mouse (probably when he is not doing something / or even when he is doing something) and launch random applications. Would be really fun seeing him figure out how the mouse is behaving on its own…