BPDFamily.com

For example, many of them seem charismatic, engaging, etc. to people they are not romantically or intimately involved with (in a platonic setting). When it comes to their SOs, though, things are obviously different.

Are pwBPD aware of this? Is there a conscious effort to switch? Or is it all unconscious?

I would say its conscious.

The mask is on for casual acquaintances but those closest get to see behind it.

I think it comes back to their lack of self-identity and insecurities. My ex used to put on a face around different people. Her own friends, my friends, my family. She'd tell me this. If she was invited to one of my friends' bridal or baby showers, she'd tell me that she's only going because the girl is my friend and she'll put on a face until she leaves. She'd put on a nice face in front of my parents, then as soon as we left she'd pull the mask off. I think it's something they're fully aware of because it's how they've been able to survive, but I think in their mind it's totally justifiable.

Now that I think about it, she did used to talk about "survival techniques." I'd try to explain to her sometimes that that's not how the world really works. It's like it just wouldn't compute, and she'd toss out any justification just to prove herself. It's like trying to discuss Shakespeare with a tiger.

It worked both ways with my ex. Sometimes he would just adjust to any environment naturally (extremely different environments) and I believe it was sincere.  Sometimes, he did it completely on purpose and told me. I also discovered, when he did it to me, he admitted it to his confidante to whom he put up another façade. It was ever evolving. Scary. 

Yes, yes, and yes. They call it masking and it very common. I'm not positive my mother knows when she does this, but watching it is a terrifying glimpse into the BP's world, particularly for a child. I can only assume they HAVE to know, I mean it is so blatantly obvious.

My mom would be raging in the car to me on my way to my grandmother's house, we'd pull up, and almost like what I imagine someone w/ multiple personalities (now called dissociative identity d/o) would change personalities. She would put the car in park, and I watch her inhale this huge breath and almost instantly turn into this creepy fake doll like woman with the most insane grin and high pitched voice. We'd leave, get back in the car, and her body would go tight, face blank, and we'd drive silent as long as I didn't utter a single word.

It's how I can tell my mom is masking even if she hasn't been raging on me. She has been putting on that psychopathic grin and turns on that high pitched voice, and coats people in grotesque heaps of pleasantries. It's truly stomach turning to watch.