Sir you hit it right on the head!! This set off bells in me and my wife's head right now. He is a guy that comes to work late, does the minimum brush control to pass annual fire inspection, and worse of all thinks COVID is a conspiracy. I had to help him last DOT medical exam by telling him to drink a lot of water to pass blood pressure test. I'm not sure if he did but he passed.This is a delicate psychiatric issue for which there is no chance of a quick fix.
Frankly, there is little one can do, until an event comes along to provide a catalyst - usually health issues. Even then it's not easy, as these folk often mistrust the medical profession, authority in general, with a passion. Eventually he will likely need to reach out to a friend.
He does not drink water. He's a sugar soda drinker only and eat's one huge meal per day. His health is not good at all. The only time I have seen him go to a doctor is when he gets kidney stones. He then goes to diet soda for a few months then back to sugar soda. His eyes are crap!! I offered a few years ago to pay for a eye exam and he tells me the drug store magnifiers are good enough. When I point out they check out eye health too he just laughs. The last year or so I have seen a haze in his eyes that looks like he is getting cataracts. Kind of spooky considering he still drives a tanker truck and has to navigate touch screens when loading gas.
Here is his typical morning /afternoon"meal". That is a 44oz Coca Cola fountain drink on the curb. There is another 3 liter bottle of it in the trunk of his friends car for refills.
Our ride to Death Valley it was the same theme. Always a 44 oz fountain drink wedged between handlebars and windscreen. We made our different eating/drinking habits work be me filling my water bladder and having small "semi healthy" snacks at fuel stops and him refilling his fountain drink. When we stopped at night he would then eat real food with me. My whole 18 years of knowing him I have never seen him drink water or eat except at night.