Narcissists don’t like boundaries. If you set a boundary, they will usually cross the boundary on purpose, to prove that you cannot control them. It’s like a challenge to them. Then, they will tell you how selfish or unreasonable YOU are. It’s crazy making, I know.
To help me set boundaries, I got specific language and ideas from books or my counselor. I gained confidence by “sanity checking” it with another person and confirming that my boundary was wise and healthy. When my boundary was crossed and tested, which it always was, I was prepared to stick to my consequence. Sometimes that meant walking away, or hanging up the phone, or not responding, or saying “never mind”.
One of the first boundaries I set was a physical one. I needed to feel safe in my own home. When my XNarc came to my door, I practiced that I could either answer or NOT ANSWER my door. I could choose to engage or not engage. If I answered the door, I decided I was not going to invite him inside. If we talked on the doorstep and the conversation didn’t go well, then I would ask him to leave. If he didn’t leave, I was prepared to tell him I was calling the police, and close the door. Then I was prepared to go and call the police. All of those steps may seem simple to some, but because my boundaries had been stepped on SO MANY TIMES prior, and I had been told how selfish and self-centered I was, it took me some time to work through those boundaries and have the confidence that they were healthy and normal and necessary.