How can you get through to someone who doesn't take his physical life seriously?

I’ve known my cousin son since he was born. He’s 20 and going to be 21, maybe. He is diabetic and has been since he was 5 years old. He doesn’t moniter his condition without people being on top of him at all times. He’s more concerned about parties and shopping and friends but doesn’t have time to take care of himself.
He’s ended up in the hospital at least once a year because he did something foolish to raise his sugar or because he did the opposite.
Found out today he is in a diabetic coma. Luckily he will be alright but his organs were going into athropy. No matter what he always seems to act like everyone else is over reacting and he always acts like its no big deal. He milks everyone for sympathy for a while till the next time.
I just don’t have it in me to be sympathetic.
I understand what its like to be born with a condition that seperates you from the rest of societies norms but I don’t think that is an excuse to be a total irresponsible with your life.
Is there possibly something I am missing that can help him see how important his health is?
Or doesn anyone with diabeties know of any programs that might help.
Sorry this is so long but I am just so fustrated.