There are different types of behavior with BPD. There are those who predominently act out (raging) and those who act in (cutting) and there is a continuum with sufferers somewhere on a spectrum - low functioning (prone to drug use and poor societal function, crime, and hospitalization) and high functioning (can hold down a job and "appear" normal to people not close - like family - to the BPD.) Higher functioning BPDs almost universally deny that they have a problem. My opinion of higher functioning BPDs who predominently act out is that they lack a conscience and are self absorbed.
If a BPD is higher functioning and intelligent, they often have the ability to "read people" pretty well. They can also be extremely adept at manipulation. It's very easy to not understand the manipulation, especially when everyone else around (i.e. not family) seems to think well of the BPD. The manipulation and the lack of insight from others can make the non-BPD doubt their own instincts.
At the core of all BPD behavior is fear of abandonment and great difficulty dealing with their feelings.
CONTROL is at the core of effective, manipulative BPDs. It's a sick game, but it gets played by many women. BPD is the most prevalent personality disorder and yet most people have never hear of it. Statistics show that just about everyone interacts with a BPD at work or school and is completely oblivious.
Psychology hobby + I've known a few BPDs