I have the diagnosis, although I think C-PTSD is the more approriate term for me, personally, since my issues are rooted in lots of varied abuse and neglect.
Personally I'm one of the quiet types, whose issues are turned against myself. I do self-harm, have an eating disorder and a host of other unhealthy coping mechanisms, but I keep these quiet and invisible for the most. I don't have huge ups and downs in my emotions, and don't tend to show them if I do. I have a very hard time trusting people, which means I just don't interact a lot with people I don't know very well. I do get some abandonment issues, but mostly just emotion-wise, and with regards to my therapist and occasionally DH, and I'm self-aware enough to address these like a grown up.
I have also been close friends with two individuals with a BPD diagnosis. These, too, had a massively horrible history of abuse from early childhood.
Friend 1 I knew when we were both still quite young. She did come across as manipulative and histrionic, which was hard to understand and take at the time, as I had little knowledge of what this diagnosis really meant. She was a difficult friend to have, as a minor thing (to me) could often cause huge upset and a dramatic emotional response from her. But she was also the only friend who never judged me on my own unhealthy issues, who always tried to understand and was there for you. We sadly fell out because she fell into a very abusive relationship, and I fell out with her BF.
Friend 2 has only got her diagnosis now in her 50s. She has always kept all her issues bottled up, taking things quietly out on herself, isolating herself, telling herself for not coping with "normal life" etc. There is nothing in her usual day to day demeanor that would make one suspect anything other than depression. When she's unwell, she withdraws and isolates herself. But she, too, is a wonderfully caring friend, who I can talk to about anything. We don't have an intense, close friendship (like I did with Friend 1), but what I think is a healthy adult one, where we're there for each other when and how much we can, but living our own lives, not in each others' pockets.
There is obviously a massive amount of stigma wrt this diagnosis. Many, if not most, people will assume people with the diagnosis all "act out" noticably and can't have healthy relationships (certainly not true in my case), blow hot and cold and have extreme reactions to things. I know that can be true with some (I've known a lot of BPD sufferers online), I don't think it's the majority, especially as the individuals get older. If you have any intelligence, you do learn in some point how others will react to you if you behave in this way, and you turn the stuff inwards, at yourself, and learn to put on a mask and function with others.