I like practical jokes. Sometimes I play jokes on my staff because I know they perceive me as the stiff, always serious manager type (they didn't know me before I became the IT manager).
Two years ago I wrote a short bash script and set it to execute for a few sysadmins after they logged in to one of our systems. I then created fake support tickets claiming that the host wasn't functioning properly and made sure to assign those tickets to the unsuspecting sysadmins. I had a few laughs watching them watch their screens as it appeared that some unruly malware was operating before their eyes.
It was even funnier because I made a point to highlight the fact that the host had been "hacked", something no self-respecting hacker would ever do. Still, some of my sysadmins dropped a few bricks until I assured them they were safe. They then took delight in helping me scare other sysadmins.
For the upcoming April Fool's Day, I'm posting the code I wrote.
NOTE: The signal names that I trap may not be correct for your platform. man kill is your friend.
CAVEAT EMPTOR: Don't use this code for your own enjoyment unless you know what you're doing. I have no sympathy if you "hack" yourself. But I will have a few laughs about it.