How should I get this to stop. I start getting crazy scared because of when D-day happened and he kept trying to break door down.
They have a choice: they can live in my new world, or they can die in their old one." — Daenerys Targaryen
Look; he's a teen. He's going to have to learn to deal with difficult people, so don't try to intervene with him and his father. It sounds like he has him figured out already. As for fearing that he'll break down your door, just call the police. If it's your residence, and he's unwelcome, let them deal with him.
Sad's advice is spot on, as usual.
Married: 11 years, no kids
The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low, and achieving our mark. -Michelangelo
I just hate it though. Tonight we are going to the movies and sushi. We will have great fun, but I just hate that STBXH is even in this day and my thoughts.
If this interests you at all, "Don't Shoot the Dog" is a great, easy to read book about behavior modification. Mostly centered on animals, but it works on people, too!
You may be interested in "extinction burst" which is when things get worse before they get better.
But it is really interesting how behavior modification techniques work across species -- including ourselves :) The only way I have ever been able to permanently change my behavior is using techniques I perfected with the birds!