I found a wasp nest in a computer a neighbor used in his garage for reference manuals. He never knew it was in there until it stopped working... a few wasps flew into the PSU and jammed the fan, so the PSU overheated and according to him, went out with a bang. I wish I had pictures, but that was before I had a digital camera... or, now that I think of it, I didn't even have a 35mm camera then. It was amazing... they had started nests in two places, one in between CD-ROM drives, and one on the bottom of the hard drive that was about the size of a softball.
And I gave my brother my old K6-2 333 Mhz based computer... first, he unplugged his printer without unscrewing the little screws, and ripped the port right off the motherboard and pulled it out with the cable... never knew he did anything wrong since his new printer was USB, lol. Then when he was putting a USB 2.0 PCI card in, he noticed the fan on the CPU was blowing warm air, and touched the heatsink, noticing it was hot, and must have thought "wow, that's fuggin hot, I better take this out of here before it fries something" so he did and that was the end of that =)
Then, with his new XP2000 system I built for him, he plugged a USB cable in the front USB port the wrong way, forced it and broke the plastic indexing tab, shorting out the USB header on the motherboard which also took out the soft power switch on the motherboard, so he now turns his computer on with the switch on the power supply
Oh... and he's on his 3rd keyboard and 2nd mouse because when he gets frustrated he either hits something or throws something. Thankfully his 19 inch monitor isn't within an arm's reach where he has it positioned.