Er, um, well... Wired's gift to you - Top 10 April Fool's Pranks for Nerds.
I just pulled #4 on a co-worker.
4. Optical Mouse Confusion This is an update of the old mouse-ball-removal trick: A small piece of tape over the laser sensor on an optical mouse will cause it to go haywire. Just color the nonstick side of the tape with a Sharpie and then tape it over the lens.
A Wired.com reader last year reported that someone at a major tech company (it rhymes with 'Frisco') was fooled by this trick four times in a single day. Sometimes the simplest pranks are the most enjoyable.
Might have screwed up his day, but I loved it. I'm gonna do it again to someone else. In other related news, they may find my corpse in a ditch later today.
And if you really hate your co-workers, open this image full screen on their pc.

Once they realize their monitor's not cracked, they'll thank you for showing them how futile it is to be attached to earthly possessions.