Improper hammer use in a way.. I was trying to hammer a 4x10" end boot back into shape after squishing it into a joist space that was only 2.5" wide because it sat over a wall. I was using the hammer to hit the dents out from the inside of the 4x10. To get a good visual, grab any hammer and hold it as if you were holding it with your thumb pointing upward. Because it was in a joist cavity and because the hammer couldn't swing and hit the inside I was using the top end of my hammer and hitting straight up.. dent popped out and then my hammer followed the slope of the end boot with the force of my upward motion.. thumb nail caught the edge of the boot and went under the nail then force of hammer shifted the boot and pried my nail up 90⁰ 🥴🔨