How do you react to his uncleanliness? I used to argue with my son about it and tell him to do things like a child. It ruined our relationship for quite some time. I’m doing things differently now and slowing rebuilding what was broken. I talk to him now like a friend and with respect, being very careful with my words.
I am using examples when I can. I had chemo a while back and because of it am experiencing issues with my teeth. I show him what is going on in my situation and I see him thinking about it. Now he is starting to use Neem (alternative to toothpaste) and brings it up that he is doing so. I nod and just say “nice” and leave it at that (I avoid the “I told you so” tone entirely now). I don’t berate him about things, society will do that for us.
I think men, and these are men, not boys, stop caring when they lose their autonomy. My son was depressed and those are symptoms of depression. When he started coming out of his depression, he started caring more about his appearance. Don’t get me wrong, its far from where he needs to be, but its a start.
I also work with homeless people frequently at my library and every once and a while, I’ll throw in an anecdote about one of my patrons and how sorry I felt for him because he was in pain due to his teeth. It gives him something to think about but I’m careful to put space between my stories and fill the rest in with praise and lots and lots of love. The other week I told him I really liked the clothes he was wearing and that he looked handsome - he wears that outfit all of the time now, but I know he’s listening.
Pick your battles. Good luck.