Why do those with BPD hold onto their anger for so long. They appear vindictive. What's up with that?

Answer 1

The simple answer is that anger is a response to pain (think of when you stub your toe on a chair and you get angry at the chair) and it feels stronger and safer to feel the anger than it does to feel the pain. The anger also allows you to blame others for what you are feeling and see yourself as a victim rather than to feel the enormous pain and self-doubt that usually comes from rejection.
A more complicated answer lies in understanding how Borderline Personality Disorder is born. Rage comes from repeated experiences of being shamed, usually as a very young child, by the people the child depends on to care for them and protect them. The child needs to maintain the bond with the caretaker, as they are dependent on them, often for their very survival and it is unsafe to express this rage at the caretaker's abusive or neglectful behavior. In order to maintain the bond, the child splits the caretaker into good and bad aspects-the good nurturer who they attach to and the bad, shame-inducing perpetrator who frustrates them. This polarized view of people then characterizes all their subsequent relationships and the person reacts with either idealization and worship (for the "good" person) or rage and retaliation (for the "bad" person), depending on which aspect of the internalized image is being triggered. Often each significant person in the Borderline's life suffers both of these reactions depending on whether they are gratifying the individuals needs or frustrating them at any given moment. Borderlines bounce between extreme dependency on others (because the internal ability to self-soothe never developed) and terror at being contolled/smothered by the other person and they often use rage as a way to regulate distance, both when they feel too close and smothered or when they feel abandoned and rejected.
This is an extremely oversimplified explanation that tries to address your question about rage, but there are many other dynamics that play out in Borderline Personality Disorder although seemingly unprecipitated rage is the characteristic many people recognize and associate with Borderlines, but it's really only half the story. For a really excellent and easy to read book on the subject, read "I Hate You, Don't Leave Me". I have consistently recommended it to most all the Borderlines I have worked with in therapy as well as to those who have found themselves in relationships with Borderlines.

Answer 2

Because they are nucking futs! I have a niece who is BPD and she has totally destroyed everyone in our family with her lies and her stealing and her using and her false accusations and her manipulations and all her evil ways...she needs to be locked up permanently, but instead she roams free, destroying everyone in her wake...