Sounds like it could be a stim thing - impulsive, you say? Any chance there's (undiagnosed?) ASD there? The mentions of bitter spray reminded me of when my mother tried that to get me to stop biting my nails. I just stopped using my lips and tongue, and only used my teeth...
Anyway, if it's a stimulation thing, maybe finding an alternative would be easier than getting him to stop entirely.
I understand why you'd go there when it sounds like other options have been exhausted, but I don't think it would be a good idea. Seems like calling the kid out like this would only open up opportunities for bullying, without doing anything to address the source of the issue.