Hi growingstonger, I am also a mother with young adult children. I know how difficult it can be. There have been times where I have had to step back from each one of my children when they were behaving in disrespectful ways towards me. It wasn't easy, and it was damn painful.
I agree with the the other posters that said it's best to set some boundaries with your son. You don't even have to tell him what those boundaries are. You just have to live by them to give yourself peace.
Examples of some boundaries:
"I wont talk with him on the phone if he is being disrespectful"
"I wont allow him in my house when he is being aggressive"
"I wont do things for him he should be doing for himself"
"I wont lend or give him money if he has been irresponsible with his earnings"
"I will not engage in circular arguments"
"I will not lend him my vehicle if he drives like a jerk"
Of course those are only examples, and may not apply in your situation.
It is so much harder being a mom to young adults then I ever imagined it would be! My heart goes out to you while you go through this struggle with your son.