I was using a Mini Griptilian to shave some excess off of some detail molding during a custom cabinet install. I grabbed a short piece of molding, and holding it from the base, went to shave down it toward my thumb.
I remember thinking, "This is stupid. Always cut away from yourself. Nah, I've got control of the knife, and it's just a l--" that's when the knife slipped and did a riposte down the edge of the molding, right into the side of my thumb and stuck in the nail.
Wasn't really a bad cut, but it took some doing to get the blade pulled out of my nail. I had to hurry it outside, away from the client. Partially to keep the blood off the floor, but mostly because I felt like an idiot, and didn't want to answer any questions!