Well what if you broke the guys arm instead, because chances are he doesnt know how to properly wield a knife. And instead of stabbing him, you break 4 of his ribs per side of his body. So that for the next 4 months he cant sleep properly without severe pain, knowing that he fucked around and found out. There are worse things than stabbing that are way way more painful, and easier to get away with in the name of self defense.