Walking away quietly is sometimes the loudest boundary available.

Leaving without a scene is often more definitive than any confrontation, because there is nothing to argue with and nothing to resolve. A dramatic exit gives the other person something to respond to and a way to keep the conversation going. Quiet does not.

If you need to end something, consider ending it without the final speech. Say what is necessary and no more. The absence will communicate what the argument would have obscured.