If situations come to the point that you must draw the line.
Then hold that line.
If you fail to follow through and hold whatever caused the line to be drawn to account, then you, not them, are the bigger problem in the room.
Deal with situations that won’t go away. Be clear, no adjectives, no emotions, just the facts. State the followup and define the line.
And hold it. Follow through, for good or bad, follow through.