Have you eve been around someone who seemed to get mad or upset with you all the time, not matter what or how insignificant something was?
All you can do is love the person. And point out in a loving way when they are being upset with you. Point out in a loving way how they feel now. Ask them in a loving way if their anger is working for them? Do they enjoy the outcome of this.
Right now I am having the opportunity to remember this.
It does absolutely nothing positive to get angry back at the person, no matter how justified it may seem.
Because when you are loving in the face of someone else being angry at you. It makes it really hard for them to hold onto their anger.