Not my last, but certainly my best and definitely dumb. From a couple of years ago when PCG asked about PC building horror stories this was my offering. At the time it was no laughing matter , but now, of course, it's great to tell at parties.
My very first PC was a 486 DX2/66 and it was housed in a case that was so heavy and thick it could possibly have withstood a nuclear blast. One day I'm on the floor with the system digging into its guts for one reason or another. I can't remember exactly what it was I was doing but it was pretty challenging to get something in or out of the case and it caused the heavy case to start to tip over.
I stuck out my leg to catch it before it fell, and the inside corner of the case caught my knee. I was wearing jeans that had holes in the knees so the metal part caught bare skin and some sharp edge dug in and made a nice gash across my knee requiring 11 stitches.