I cant count how many times over the years. The worst and most stupid was back when I owned a commercial sound and lighting company some ten years ago. We were working nite shift on a job and it was about 2am and very cold. The truck was parked far away from the work area and I needed my KO kit. I had my hole saws inside with me. Well I crawled up a ladder to make my hole in this LIVE 400a three phase panel. I pulled the conductors in the gutter out of my way and pulled the trigger on the drill. My intentions were to yank the bit out as soon as it went through but that didn't happen. The bit caught some conductors and it blew out of the drill and landed between legs B and C on the line side. Big blue arc... Me on ground... 1200a main tripped... Everybody in the dark.

Dumb, dumb, dumb.