ok, I'll share my "I let the magic smoke out moment".
I used to work in PC repair and got all kinds of free computers to tear down and build franken-puters out of.
I had gotten some Dell PoC beige office box and had stripped it down. Everything in it was fine and I grabbed the PSU and never thought about it. Months later Im working a board, Pentium II something or another, nothing fancy and I grab this PSU out from under the breakfast bar in that apartment. Well I wire everything up and I'm going through the lines and making sure I don't have a molex stuck to a jumper pin or whatever and I see a 4 pin lead that was not a standard connector. I remember that Dell had a riser card for it's ISA slots going in sideways and figured it was for powering LEDs or whatever.
So I power up this board and I get a monitor signal and its doing POST and I look over at my now ex-girlfriend and state the words:
"what's that smell?"
Shortly afterwards the board sparked, smoked and made noise and I snatched the power plug out of the wall.
Thereafter, at anytime I would dare mention my experience, prowess, skill or knowledge of computers in any context, my ex would utter the words while smirking "what's that smell?"
The little blue sparks across the 486 motherboard when I dropped a piece of RAM and had forgotten to unplug it was far less damaging. I ran that machine afterwards for months without fail. That one Dell power supply though, turns out they had an extra ground on that line. We didnt have internet in that apartment, so no looking up the pinouts in those days... <sigh>
Update!!
Since writing this I discovered scientific evidence for this occurrence:
https://hackaday.com/2016/11/03/specifi ... nt-3254751
I did that—once—and never forgot about it. 
