Reply #7: You are making an error in judgement:

[H2O Man]

When you say the ex is not physically threatening, you are making an error in judgement. I worked for decades as a psychiatric social worker, including years of forensics, much of it involving family violence. The key things is boundries. This person, as described, has no boundries. His physically being at your door is intended to convey what message? And it comes in what type of language?

You have to be able to read situations. The relationship between your friend and the ex-spouse obviously was co-battering. It isn't important for you to decide who is right or wrong in the past. But the ex was clearly in the wrong here.

The behavoirs that you take in response will serve as a model to the young person in question. You can't avoid that. So you'll either be a good role model, and respond to the situation correctly, or you'll reinforce the parents' unhealthy behaviors.

Call the police. File a complaint and follow through.