Well, I a) don't have the time right now, and b) hesitate to speak of those types with whom I do not have extensive experience, but quickly-- I'd imagine it would revolve around someone making them face their worst fear. Like how I showed my stepfather I'd always be there to exacerbate his fears of anger and disruption of his inner peace, and he couldn't move beyond that. I guess for a 4, that would be about having been threatened with being seen as common or inauthentic, for 5s having been threatened with being made to feel stupid or useless, with 7s being threatened by someone who may expose their bullshit or face the things they'd prefer to avoid. (Other types, feel free to correct me).
Things I personally am unforgiving of are betrayal--even if I eventually reconnect and interact civilly, some part of me will always be distanced from you, and if we get into an altercation, the first thing I'll remember is how you once betrayed me, and you will be reduced to that. Also, people who need to assert that I'm a poser who's secretly "weak" (one guy did that to me recently, and I swear I'm going to get him for that. I'll never forget the horror and humiliation I felt as he ravaged my psyche to prove his small-minded point. Yeah, he was also an 8, convinced I needed him to get my life in order).