I relate to the "quiet borderline" description too. All the anger and rage and hostility is there, but it is locked inside, not turned against others, at least not in ways that they can see. Some of us have had to hide all of that, and can be very good at hiding it. It's hard to find it again.

Just as an aside, all licensed mental health professionals can diagnose. Some prefer to avoid categorizing people, and some are reluctant to tell the client the diagnosis for various reasons, but insurance generally requires a diagnosis in order to pay, and every therapist needs to conceptualize the symptoms in some way. Mental health diagnosis is subjective, though, and from one clinician to another, regardless of training and qualifications, there is not always agreement. I am a master's level counselor, and depending on which setting I am working in, generally the first thing that I do with a new client is an assessment and diagnosis. I don't necessarily share the diagnosis with the client. It depends on if the client asks or shows interest, and what benefit there would be to the client. Quite a few don't want to be categorized or diagnosed at all. Some clinicians tend to consider family dynamics, etc., rather than individual diagnosis. But if there is treatment, there pretty much has to be some diagnosis. That includes psychotherapy, as well as medications. A medical doctor who prescribes an anti-depressant has to diagnose a condition that he or she is treating with that medication. Referral to psychologists for more thorough psychological testing is an option and can be a very good tool for ruling out or refining diagnoses, but isn't required in most cases. And isn't necessarily conclusive, either.