Well, not an injury to me, but I once lent my knife to someone... Big mistake!
Was checking out at Blockbuster, and the guy behind the counter was struggling to get a DVD open, but it had some plastic lock on it, that there machine wouldn't disengage. Well he resorted to trying to cut it open. I can't remember what it was, a key or dull knife, whatever it was it wasn't working. Instead of taking the DVD from him, I gave him my knife so he could get it open. It was just too painful to watch him saw at it with whatever he was using. Big Mistake!
He made a cut or two. Set the, still open, knife down on the counter. Fussed with the DVD case a little. Then picked up the knife to make another cut. He used his index finger on the "spine" to add extra pressure to the cut. Problem was, he picked the knife up upside down. Well, being upside down, it wasn't the spine he was pressing on...
I just sharpened it that morning too. It filleted him open like fish.
I saw the whole thing unfolding, and was just about to stop him and do it myself because he was working too quickly and obviously didn't know how to use a knife properly or safely. Well, it all just happened to fast and I was unable to intervene.
I felt bad, but what could I do? I know I'll never let anyone, I don't know, use one of my knives again, that's for sure!
ETA: Wife just walked in and read my post. Her comment on remember that incident: "sss, that was bad. That was bad."