I have done more than one really dumb thing, ( especially since I used to service tanks) but this is the funniest. I was changing out a UV bulb for a customer and fortunately they left after I got started. The water through the UV sterilizer came from a penguin powerhead using flex tubing. So all I had to do was take the tubing off the nozzle of the powerhead to service the UV. Well, when I got the job finished and the UV sterilizer back in place under the cabinet I flip the on switch. Oops, I had forgotten to put the flex tubing back on the powerhead and it shot water 20 ft across the customer's dining room straight into a wall outlet and tripped the breaker! Oh man, what a mess. I cleaned the water up in the dining room first and the outlet as best I could. Then I went down into their basement, found the breaker box, and found the tripped breaker. I flipped it back on and it was ok and the customer doesn't know to this day (15 years later) what a really dumb thing I did. LOL