USB PC Prankster:

The USB PC Prankster looks like a stock flash drive, but as you can clearly see above, a few toggle switches enable it to become quite the headache. Once plugged in, the unlucky PC that it's attached to will have its Caps Lock enabled and disabled at random, see garbled text splattered about quarterly reports and be victim to uncontrollable, erratic cursor movements.

Sounds like a great way to become the Most Hated Man In The Office.