Here is my most embarrassing story. It is not very security related, but it is fun!
I once worked at a small long-distance phone company as a junior IT tech guy. One day, there was a power blackout in the city. The company had its few servers on a central UPS. The UPS kicked in as it should, and we got through the blackout.
But then, when the city power came back on, the UPS (which wasn't used or tested or monitored or anything - it just sat in the back of the room, humming) didn't appear to stop supplying power. The bar graph on it kept ticking down, instead of stabilizing like it normally did when the city power worked.
It was an old UPS (I don't remember what model or manufacturer), and it had a large turn dial on the front to turn it on/off.
I was told, over the phone by a senior tech, to turn the dial to another position to see if it would stop discharging. Ok, sure, no problem.
Now, the dial had a handle with a little red triangle on one end, and the other end was about a foot long. Around this handle-dial, were various states of on/off/discharge/disconnect/etc. Many power states.
Now, I briefly looked at the handle, and I turned the long end (WITHOUT the red triangle) toward the OFF setting.
And the power shut off to every server in the building!

Yes, the red triangle is what pointed to what the UPS would do, not the long handle end! So, I managed to do what the blackout could not do, and that was bring down the office! I turned on a kill power mode that disconnects all power to the machines. Oops!

It was estimated that doing that only cost a few thousands of dollars in lost revenue.

But, they did not fire me over that! Accidents happen, they decided. I was STRONGLY told to make sure of what I am doing before I start turing dials and such.