Hi D.;
I, too, have a 14-year-old ADHD son. In Middle School we had issues with having to constantly remind him to shower, use deodorant, etc..., however those issues cleared up with peer pressure (sad, but yes, I was certainly happy when he wanted to smell nice like some of his friends and then there was the girl he liked: that's about all I'm in favor of peer pressure for). He just has to look and smell good, now. As for the brushing of the teeth, he has just recently gotten better, I still have to remind at night and on the weekends.
The hardest part is your line that he doesn't seem to care or want to change. As all of us parents know we need to find the soft spot that makes them want to do something. The incentive that sparks them to start working on whatever it is that needs be changed (hygiene) or completed (chores).
I've discovered with my son that it happens to be good old fashioned grounding or even better money. I used to try and make the punishment fit the crime, but that didn't do anything but cause more stress, for example, if he left his dirty clothes on the floor, I wouldn't pick them up. My thought was that he would eventually need something clean and finally pick up the mess and move it to the laundry room, nope. He would just wear something out of the pile. One day I did all his laundry and then stuck a note on the top of the pile telling him: "Dirty clothes stink. When clothing stinks people avoid you, yes, even friends. When clothes start to stink and lay in a pile on the floor they get damp. Dampness breeds mold. Laundering doesn't remove mold. Moldy clothes get thrown out. Once clothing gets thrown out due to mold, YOU are responsible for buying a new piece of clothing. Yes, it will come out of your allowance. Yes, that means that you won't have money for the movies. No, mom and dad will not front you the money. MORAL: Pick up clothes, keep money."
He actually started trying to do better with his laundry. He didn't always get them to the laundry, but he was making an effort and I didn't even have to say a word. When his laundry pile started to get big again, I just reprinted the letter and wrote REMINDER at the top.
We have had to dock his allowance when he broke my cell phone. The only way that he realized how much it stunk to have no money was for me to hand him his allowance (if I would have just withheld the money he wouldn't have felt the 'pain' as much) he then had to go mark off the amount on the paper and then had it back to me and do the math of how much he still owed. He was super happy when he finally paid that off.
Also, grounding him from something that he had been looking forward to for a full year really made a huge impact on him that mom and dad were done being micromanagers.
Basically, if you've made it this far through my long-windedness, find what will prompt him to do what you need him to do and follow through. If it's money, give him a reminder and then start docking the allowance. If it's his game system that he loves, take it away, he can earn the system back for consistent behavior and then earn games back for consistency as well. Also, try reminding him that he is turning into a man now and he needs to be more responsible for himself. That seemed to give our son a bit of encouragement toward making some better choices (not always, but a bit better).
Hang in there and know that eventually he will start getting the hygiene down.
DJ