When I bought my house, I had low water pressure. Thought that was the way it was. About 3 years later, had a plumbing problem and plumbing guy couldn’t figure out why the well kept running. Turns out there was an outside faucet that didn’t work because it was broken off 3 feet under ground. I’d been doing the equivalent of running a hose wide open for about three years. Plumbing guy said it wouldn’t really damage the pump because the pump never turned off (turning on/off is more work than just running) and laughed as I did happy dance about all the new found water pressure.
Left an LP spinning on the turntable for a couple days. It may have damaged the needle, although I never noticed any deterioration in music quality. Since it was just spinning around on the inner, non-playing tracks of the record, none of the music was harmed. But…dumb.
When I was in grad school at the University of Wisconsin, I had a graduate assistantship with a department of the University Extension (in an office of about 20 people). I was working on a Friday afternoon, and, at about 4pm, the secretary stuck her head in my office to tell me that she was leaving, which made me the last person in the office (and meant that I was responsible for turning off the lights and locking up).
What I didn’t realize is that my boss (who was a chain-smoker and heavy-duty coffee drinker) had made a fresh, full pot of coffee on our automatic coffee-maker at around 2:30, had drunk one cup, and the rest of the pot was still sitting on the warmer. I didn’t even think to check the coffee-maker when I shut down the lights and turned everything off at around 5pm.
I came back into the office late on Saturday afternoon, to work on writing a paper. The entire office smelled like burned popcorn, and I quickly discovered the coffee carafe on the warmer. That 10 cups or so of coffee had been burned down into a 1/2" thick layer of tar on the bottom of the pot. Thankfully, it didn’t break, and a few minutes in hot water was enough to loosen the tarry residue, but the office reeked for a couple of days.