Tried to prove to my mate that a piece of glass wasnt sharp (I was very drunk...and it didnt look sharp). To do so I pushed it into my skin and dragged it really quickly. Cue blood everywhere, tendons/bones showing, an old lady nearly having a heart attack when I turned up at her door to ask if she had a spare towel...and a very angry father when I got home.
And a huge scar to this day