I still think for us that it is less of a doorslam and more of a click and a forever locked door. There isn't much hurt or emotion fueling it. Just a desire to be done with dealing with someone who is either untrustworthy or stuck in a an unproductive pattern of behaviour. I think it rarely happens in a moment of anger. Just something snaps and there's no desire to keep trying. I don't think INFJs give up people in their life easily who matter to them, and they don't get terribly emotionally invested in the the ones who don't matter to them.
In the first case, I had written for about five years to this guy and had dated him briefly the first summer when we met. We lived far away from each other and there was no interest in dating again later on. I was more mad at him for his girlfriend's sake and because he wasn't being honest, rather than upset because of how he and I interacted.
In the other case, I had known the guy for three or four years, written regularly and talked on the phone regarding a major project that I did and needed his expertise for, and became friends, emailing regularly. Again, the issue was that he had not been honest in his intentions and had outright lied. That would have been less of an issue if it had only involved me, but I was embarrassed for convincing my mother to spend the money to come, had booked return tickets expecting that we would need two weeks in the area where he was and had hauled along a lot of unnecessary equipment. He had known from the beginning that he did not have the information needed, I was embarrassed at my poor judgement, and I had practical concerns as well.