Fun story: shortly after my dad died, my brother was visiting. While he was in the basement, he plugged an extension cord he found into an outlet. All of a sudden, a weird smell permeated the house. I realized what was happening, ran out to the circuit breaker box, and turned off the power to the basement. My dad had wired up that cord and outlet such that if both ends of the cord were plugged in at the same time as the light on the front porch was on, it would cause a short. Of course I knew this was a bad idea and told my dad it was a bad idea when he did it, but he wasn't one to take my advice...
(That doesn't excuse my brother, though. If you see an extension cord and you don't know what it's doing, don't plug it in.)