I've done a few stupid things over the years, all of them should've been avoidable.
One time, I was in a rush to boot up my A2000 and I put a floppy disk in upside down. I waited a few minutes for it to boot before realizing I'd the thing in wrong. Amazingly, the floppy drive still works to this day except for the eject button. I've to use a pair of tweezers to take disks out. Over 15 years old and still working.
The other stupid thing I did was throw away the 2mb Chip RAM SIMM from my A4000D. After I'd moved to a new house, the machine wouldn't boot. So, I opened it up and started swapping components to see what was the matter. Somehow I got it into my head that the SIMM was bad and threw it away. That's the only piece of computer hardware that I've thrown away in the last 7 years! It turns out that during the move the case became warped, and I didn't realize it until several days later. So, I'd to buy a new case, and use an 8mb SIMM for chip RAM, and there was most likely nothing wrong with the original SIMM.
Not Amiga related, but I've nearly killed myself several times while trying to wire up power switches on old AT PCs. Always unplug it.
Not as exciting as sparks and flames, and melting chips.