As a pre-teen & teen, I mowed lawns for a living, and could not afford to buy mowers, so I built up a stable of junkers that other people had thrown out for various problems. One was in decent shape, but would run absolutely wide open at all times.... no amount of tinkering could slow it down.... it was hell on tall grass, so I ran it that way, waiting for the inevitable "bang". It was shut down using a metal lever that was pressed over against the end of the spark plug. One day while mowing a wet lawn in a light, misting rain, the owner's beautiful, scantily clad teenage daughter came out to just to tease me. Being a horn dog, I of course decided to go hit on her. (See where this is going?)
Smiling, never taking my eyes off her ample assets, I cooly reached out with my wet tennis shoe with the large hole over the big toe to shut down the mower.... and stuck that spark plug end right through that hole in my shoe.
The world went very bright, I experienced pain like I never imagined for something approaching eternity, and woke up sometime later on the ground.
The mower was still running, I had wet myself, and the girl's mother (also gorgeous) was slapping my face trying to revive me. After a few moments i regained enough muscle control to stand & shut off the mower, reassuring the woman that I was OK. (I was not) The woman made a comment about "That stupid garden hose always soaks her when she does yard work too." I weakly finished the lawn, grabbed my gear & left, later realizing that I had failed to collect my pay. I was too embarrassed to go back, so I turned the job over to one of my competitors, who collected my fee and paid me.
The only lasting effect is that the image of the girl in that instant appears to be electrically etched into my brain, not a bad effect at all....