My Dad tells a story about a neighbor who used to have a truck with a flathead 4 cylinder engine (sparkplugs in a line across the top).  

This guy was known for being extra tough...  Sometimes he'd show off by grounding all 4 plugs with his hands to stall out the running engine.  It brought tears to his eyes, but he'd do it.

I knew him when he was in his 80s and I was in my 20s- I would not have wanted to cross him!