I've read your post 3 times and unsure what your saying.
Alcohol (with or without diabetes) can change personalities and make people argumentative and defensive, I think if his drinking is causing problems then he should leave it well alone, alternatively he could ask for guidance from his diabetes care team on the do's and don't when drinking, alcohol can have a lowering effect on blood glucose levels which can lead to hypo's, when people are hypo's then can act out of character.