Clearly a knife failure: I had a Kershaw Scallion where the linerlock failed - I was not cut too badly, but I never trusted that knife again. (Not a huge loss, because I never really liked that knife anyway - just not my thing.)
Just really poor quality: My CRKT Folding Razel chipped (quite a large chunk knocked out) on the square end the first time I ever used that part of the blade. (Also, the main edge on that knife could go from sharp to dull just by looking at it funny - I swear the blade must have been made of raw iron.)
Really, my fault, not the knife: As a kid, I broke the blade off at the tang on a small, single-bladed Buck slipjoint, but that was my fault, using it badly. Good lesson learned.
Not a knife failure, but somehow reminded of this, so decided to include it anyway: I had a Kershaw D.W.O with gray handle that took a walk from my workplace 30+ years ago that I've always regretted not replacing. I see them for sale occasionally, but I've never seen another gray one - it seems like they are all either orange or black.
-Tyson