when I was 16 I got my first '57 Chev, all original 150 model 4 dr with a 283.  Those were the days before inductive timing lights, so you had a small spring you hooked to #1 spark plug, your timing light hooked onto it, and the spark plug also hooked onto the spring.  So with motor running, I figured I was done setting the timing and reached down with both arms to disconnect the spring, etc  -- ZAP.  Both arms flew up, the left arm hitting the radiator support, and the right arm hitting the hood hinges and hood.   I got a good jolt, and both arms had their shair if scrapes and bruises.  Never made that mistake again.

You can also tell I'm right handed, as my left hand has its share of scars from tools slipping and gouging my left hand.   Good one was scraping the gaskets off a big block manifold.  I was holding the end of the manifold with my left hand, scraping with a putty knife in my right hand.  Something slipped, and the putty knife imbedded itself in my left thumb.  Never bothered with stitches, so I ended up with a larger scar than was necessary.