Hi! Thanks for writing in, this is a good question that a lot of people probably have.
The first thing is to figure out what is setting him off. What makes him angry? Is it something he hears or is it that another resident annoys him? Once you know what makes him mad, remove that stimulus.
It’s helpful to bring something in when you go to visit. Can you bring a pet dog or another animal to see him? What about a photo album or even something you baked? It will give you a conversation piece and probably put him in a good mood.
Finally, the best thing you can do when he gets mad is to smile. Be calm, remember that it isn’t directed at you, truly, and try to change the conversation. There are going to be times he gets upset, but it’s just a part of his disease process.