For me... my boundaries are most appropriately expressed by my actions, not my words.
I repeatedly said, "I will not live with active alcoholism"... it wasn't until I packed my stuff up and moved out, that I really showed that I meant it.
I repeatedly said, "I do not like the way you are talking to me."... yet kept participating in the unacceptable exchanges. What spoke volumes was the first time XAH started screaming at me and I said NOTHING in response. I simply stood up and walked away.
With my mother, I have had so many circular conversations with her trying to get her to stop making whatever comments she feels compelled to make... I've learned that ending the call, walking away, whatever is the best way to protect me from the unacceptable comments.
The fact is - we can NOT change other people. They are going to be who they are. We have to decide what WE need to do to live our lives the way we want, and what WE need to do to protect ourselves from something that is not in line with our goals. Boundaries are OUR rules for ourselves - that's why we don't need to communicate them to others.
When we do try to communicate them to others - it's not a boundary... it's an attempt to manipulate and control that other person.