Kingsnake Biting Himself: Bad Cut on Tail

[Bogertophis]

...discourage him from biting, if this happens to be an overly-active food response in your snake rather than a physical problem.

I was wondering this too ^ ^ ^. Some king snakes have crazy food responses. But also remember that their appetite is driven by their metabolism which is driven by the warmth they experience- so is perhaps his enclosure being kept too warm & without enough of the "cool" side?

Another thing that impacts their appetite is if they're sharing meals with internal parasites (which can also cause pain, btw) so have you had his stool checked? I would...something's clearly wrong.