Start with the limit
Boundaries get confusing when they turn into arguments about whether you are allowed to have them. Start with the limit itself: “I can’t take calls after 9 p. m. ”
Use calm, direct language
Phrase the boundary around your action: “I need to leave if yelling starts,” or “I can talk when we are both calmer. ” This is different from trying to control someone else.
Let discomfort be part of it
A boundary may feel harsh if you are used to keeping peace by saying yes. That discomfort does not automatically mean the boundary is wrong.