Like...that is actual rot. That is rotting flesh and whatever in his mouth. And he doesn't see this as a problem? As something to worry about?
The smell must be...awful. I had a wisdom tooth come in at an angle, impacting against another tooth which made it hard to fully clean the other tooth. Once I got the wisdom tooth yanked, the other one had to be root canal'd because there was some decay. Once or twice in the couple of months between the wisdom tooth healing and the root canal, a little bit of the decay would come loose and I would taste it and want to vomit. And that was a tooth in the back corner of my mouth, not something at the front of my mouth that would touch my food with every bite and every sip of something would touch it and ugh now I want to throw up again.