Where do we start...
When I was very young (maybe 6 or 7) I had a fascination with car stereos and was given an old cassette player. Didn't know the difference between AC and DC and thought that voltage would be the same either way, so connected up an AC transformer from an old train set and fired it up. The radio worked for half a second or so and never again thereafter. In a later episode I connected up another car radio to a 12V drill battery. The radio wasn't fused and there was no inline fuse on the power cable. Connected it up backwards and melted both power lines.
Pioneer SA-8100 restoration, put one of the outputs back in backwards. Large bang, plenty of smoke. It was eventually restored with modern substitutes.
Fixing a cheap Sony amp that wouldn't power up due to a blown fuse. Didn't have the correct rating and the selection of small glass fuses was dwindling so opted for a jumper wire instead. The problem was in the amplifier module, though quickly spread through the power supply and even the input stage, blowing components in quick succession. It wasn't worth fixing anyway.
First ever raspberry pi project. Thought I'd see if I could at least get the thing to boot so grabbed the first power supply I had to hand. The cheapest phone charger imaginable rated (supposedly) at 500MA so woefully inadequate. It violently blew up, tripping the mains but not before blowing a few components off the pi.
Had a mint Technics 1210 in my main system for quite a while. Was playing a record one day when the platter all of a sudden spun up extremely fast, and the turntable went bang and smoked. Turned out the previous owner had wrapped the fuse in tin foil. I'm amazed it worked for as long as it did.
Newly rebuilt Thorens TD-150. Was setting up the suspension, periodically running the platter. Had the deck connected to the mains and shorted the power switch with the back of my hand. Received a nasty shock causing my hand to involuntarily fly up, nocking the plinth over, causing the platter to fall from the sub platter. Bent the main bearing, snapped the motor shaft and broke the arm in 1 go.
Marantz cassette deck. Sold it on eBay, buyer sent it back complaining that it was faulty. Turned out the mechanism had been swapped (I now security mark them when I work on them) and the solenoid that drives the mechanism was faulty as was the motor. Couldn't get another mechanism and eBay's seller protection didn't protect me at all, so I smashed it with a sledgehammer. The hammer was also used to 'repair' an LP12 with a bent sub chassis and a paper shredder that started giving out pretty severe electric shocks.
These are a just a few from memory. There have been a few more along the way, fixing things and forgetting to unplug them first, putting voltage where voltage shouldn't go etc. Some things are blown up or smashed on purpose because they've pissed me off or are beyond economical repair. off The things I build or repair do generally work for the most part though, and despite being a blind man I have never broken a stylus nor had any accidents with superglue, so I guess that counts for something.