A couple of incidents spring to mind
When in college doing electronic systems I think it was, there was this sorted of breadboarded stuff which was like lego with little diagrams of components on the back - you could plug them in to create a circuit so you had a visual representation from the top. Power was supplied by a separate box with lots of dials.
Whilst doing an exercise, there was a loud bang, looking round there was a mushroom cloud billowing to the ceiiling and across it whilst a student standing in front had a stricken look of terror on his face.
From this, we (the rest of his classmates) formualted the theory of random connections in electronis :)
Another incident when working was in a computer room early 90's and needing a monitor plugged into a headless PC. Designated monitor was on, so we thought, fine. Turned off, unplugged and plugged into headless PC
<FLASH><BANG!> - I was standing over the top of it when it bliew, the ensuing mushroom cloud billowed up and there was a frantic rush to find anything to dissipate it before it hit the smoke detectors in any kind of concentration!
That's not including the ICL 2900's that could be crashed by accidently banging into them (never done that) and EPO cable that was incorrectly labelled such that when an elecrician cut it because he thought iwas a power cable that was being removed, the whole DC went down.