Back in the days when I was at Uni, I was aiming for a Computer Science Major, so knew how to program in C, Java etc etc. I was able to create a cool program for DOS based computers that would make the hard drive search for files, but display the DOS prompt saying that it was formatting C: and counting up to 100%, no matter what keys were pressed, even the reset button was disabled.
Really nothing went wrong at all and guys had a good laugh at the end of it all.
But what was worse, was that one night after a few drinks, and a few bets from mates, I tried to reprogram the program to go into the CompSci network, spread itself through the network, and all at once, start running through the procedures mentioned above. Except in my slight inebriated state, I forgot a few lines of code, and at the appointed moment, I was able to format the Hard Drives of over 200 terminals, servers and the backups and standby units.
My university career ended at that moment.