I think my worst mishap was bench testing a load of Amiga 4000's, I was putting hard disks into 40 of them as quick as I could so I could switch them on and leave them on overnight to test them. Unfortunately in my haste I picked up an odd screw that had found it's way into my screw box, it was too long, and I didn't notice.
The screw embedded itself into the circuitbaord of a Quantum hard disk and upon powering on filled my office with that lovely, highly noxious, carconogenic orange smoke.
I did get home earlier, but only because the office had to be evacuated
I had a similar problem once before on a Western Digital and got pink smoke.
For most actual pain inflicted nothing comes close to an old IBM PS/2 Tower, this is one of the 'things' IBM produced during their venture into MCA architecture, it weight roughly the same as several small cities - and I had to carry one on foot for about 5 miles... That was painfull.
For most serious injury, I would guess it was an old 286 I opened up, it was at an installation at Stansted airport in the old diamond hanger, I can't remember the make of the computer but it had one of those horrid metal earthing plates on top similar to what Compaq now use, only this one was not part of the lid and removing it was really stiff. When my hand slipped in a vein effort to budge it I reckon it went the best part of a centimetre into my hand. That was a big ouch moment and probably the most blood a computer has drawn from me.
God created the world in 7 days, but we're still waiting for the patch.