@TheGibson Reading through the replies brought a couple of my own to mind:
I wrote a script on a Sun workstation in our lab that would play a cuckoo sound on the hour. Something was off in my logic and I came in late the next day to the box incessantly cuckooing and my coworkers very irritated.
Even earlier in my life, my boss wanted some free space on the main work computer. This was 1992/1993 timeframe. Turns out that Windows really dislikes it when you delete all of System32.