I am so sorry that you had to deal with the spoiled man/child. MLCers do this kind of stuff all of the time until they reach acceptance. They are operating on emotions only. They do not think like we do because they are emotionally driven. We would not think of raising heck about a family member not knocking and using the bathroom, but the MLCer will do it all of the time. I wasn't surprised to read how he behaved.
You did the right thing in removing yourself from his ranting. Do not sweep this kind of behavior under the rug. They are so predictable when this kind of behavior happens. First they blow up and then they come around looking like susie sad eyes wanting and hoping that they can find a way to make peace.
DnJ knows that I will agree with him 100% on the advice he is giving you. Set those boundaries and adhere to them. Do not waffle one bit. You can be kind and/or cordial, but you need to be firm when he acts out. They are teenagers even though they are far, far further along in age.
Again, I am so sorry he acted out.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.