I used to work as network admin for a small web-hosting company. The guy who owned that company also owned a cybercafe and I was expected to deal with all the problems there too. Anyway, I go in one morning and he proudly shows me this light-up sign that looks like he's found it in a skip. We had no UPS on the web servers, despite me repeatedly asking him to buy one, so I ask him not to plug this thing in until he's at least tested it with a multimeter; he knows how to do this, so I think it'll be safe to leave him in the building on his own when I left work later that day.
I go in the next morning and he's flapping around the place like a chicken with its head cut off because all the power is out. It transpires he'd plugged the damn thing in and turned it on just before I'd arrived, flipping the breaker and after I'd corrected that, the Sun box subsequently shit itself on reboot. A Red Hat box slowly went through its recovery boot while I babysat that other PoS; this was a long time pre-ZFS so it required some careful prodding to get it working again. I eventually get it all up and running after several hours, then made him promise not to plug it in again and to *buy a UPS* so *when* the power failed, I wouldn't have to do this again.
You can guess what happened the following morning: the blithering idiot had done it again, allegedly after "testing and repairing" it. We were a couple of floors up so I suggested he take a walk while I repaired it in case I kicked him through the window. I'm not a big bloke and seldom believe violence is the answer to any problem, so he goes for a walk in full knowledge that I am very angry indeed at having this entirely preventable problem occur twice in the space of two days.
A couple of days later I sign for delivery of two shiny new UPSs.
Then there was the time I was accused of stealing from a safe I'd refused to accept the code for. I walked out not long after that, unsurprisingly.