As a former insurance agent, I can help you a bit. There would have to be proof beyond reasonable doubt that negligence was involved. If they were borrowing your knife with your permission, they would have no claim. Some as if you loaned them your car and they droved it into a tree and injured themselves.
The grey area is if said knife or other object were left in plain sight where anyone could access it, especially if the knife was open or out of it's sheath. Same as leaving your car running or a loaded and cocked gun on the kitchen table.
People will do whatever it takes to prove some sort of negligence was involved. There was a guy who sued and won against Briggs and Stratton, because he picked up his lawn mower and tried to trim the hedges with it, resulting in the loss of several fingers. He claimed negligence because there was no warning label. Hence the implementation of the safety bar on gas push mowers.
When in doubt, use common sense, as most people don't.
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