In high school, my friend and I were demonstrating to Fred the magic powers of our IMSAI 8080 with ye olde:

  10 PRINT "FRED IS A GEEK"
  20 GOTO 10

To wit my friend and I would giggle and taunt.

Undaunted, Fred took a look around, found the power button, and turned the machine off. Yes, that power button next to the "DO NOT TURN OFF" sign.

As the monitor and LEDs faded to black, the giggling stopped and my friend and I stood aghast at Fred's treachery.

Fred left, and we were tasked with restarting the machine, getting to the monitor, keying in the hex code of the cassette loader, and reloading BASIC from cassette.

Got it to work on our second try!