Angry, hard of hearing Dad (86). Any advice?

Besides his hearing, or lack of, my father is in ok shape. Yes he is slower, many things he cannot do anymore. I have always helped in any way I can. In the past year or so as his hearing has worsened, he has gotten very hateful and angry. It is like he thinks he is boss not only at home but anywhere. Example- I recently had to have surgery as an outpatient. He and my mother came with me, (I am also recently widowed). He got into a shouting match with a woman as she tried to park where he was standing, he thought he had the right to stay put until I circled the lot for a vacant spot. I had no idea until this woman comes up behind us to say how rude he was and he threatened to hit her. His words were "you get outta here before I knock your teeth out" I was so shocked, my father has never been so terrible. He wanted to argue with this woman and repeated his threat until I got between them and told him that is quite enough! He was so angry with me at this point he pulled both hands into fists and the look in his eyes was just awful. I try to ask him where is this coming from, it has become a nightmare to take him anywhere as you never know what will set him off. He seems to think his behavior is perfectly in order. And the language he now uses is so not the father that raised me. He seems to be angriest with my mother and myself. We are the 2 people closet and was the most patient. But these out bursts and anger are getting scarier. I also hate the way my mother has been putting up with this. His health is not bad for 86, he has a great DR. and sees him often. It seems that the less he hears the madder he is. My mother and I have shown great respect for this man and let him know we too are effected by his hearing. Difference being we will do anything to try to keep him involved in any conversation as best we can. This angry man is not how I want to remember the father I so love. Please anyone? Any ideas?