Very odd. However there's more of his tail left than I was expecting.
The good news is that as long as it doesn't get infected, he should be fine as far as overall reproductive ability and activity. I have had baby chameleons where I had to amputate almost the entire tail, and they grew up fine and without issues. This is surprising since chameleons use their tails so much but from my experience it works out OK. If he keeps doing this regardless of your efforts, and the tail gets bitten down to even shorter, chances are he simply won't be able to reach it anymore and he will just have a stub tail for the rest of his life. Then the problem will resolve that way.
One could try the approaches above to see if that helps (hand sanitizer). You could also apply neosporin to it, which is generally considered safe in reptiles, to keep it from getting infected, while also acting as a deterrent to biting. Personally, if it were me, I would watch the tail carefully and just make sure it's not showing signs of infection. Then I'd let him keep doing it so the problem resolves itself that way, and he will either stop or won't be able to reach it anymore. Alternatively, I might just amputate the abnormal, damaged regions of the tail as needed if infection was apparent. Or, have a vet do it (probably the better approach).
Now onto some more speculation with limited evidence behind it in reptiles. Pica is a condition wherein humans eat bizarre things like iron, paint, etc. and this is suggestive of a nutrient deficiency. You could modify your supplement regimen (increase the usage) and see if that does anything. Just a blatantly speculative idea but interventions like this can work in humans with a similar condition. Might be worth trying.
Thanks for sharing!
