I think I have gotten substantially better in enforcing boundaries when it comes to friendships or people I need to deal with on a regular basis.
I won't let anyone steamroll me anymore to "keep the peace". I am firm, professional but stick up for myself. If someone "shows" me who they are once, I don't give additional chances.
I run a women's meetup group. You can imagine... .in a group of 600 women, mostly singles in their 40-50... .there are several with PD's.
One woman actually approached me and asked: Do you have issues with a lot of Borderlines joining your group?

She proceeded to tell me how her ex was a narcissist and how most of the area groups had women with a lot of "drama". At first I thought, wow, I just met someone who "gets it". I just got out of my terrible relationship and here was this strong woman, kicking ass and taking names... .
Within a week it hit me. Who tells you this stuff within five minutes of meeting you?

When you meet someone you usually talk about interests, where you are from, where you work. You don't launch into a tirade about all the "terrible" people in your life.
I would say I am significantly more aware since dating my ex. Even my ex's sister who I work with... .the first time I met her she told me how she was estranged from her father and how her child was being accused by another family member for molestation. I thought, poor girl! I felt like she must really like me to confide in me such horrible things.

This was our 1st meeting. She was showing me exactly who she is, the person who plays the "victim". Once her sister and I did not work, she spoke of me in the same manner, like I was a tormentor and persecutor.
People will show you who they are. You just have to be receptive and take it all at value.