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Phrase(s): Don’t waste your breath.
You will not get a positive response to what you have to say, so don’t even say it.; Talking will get you nowhere. • Alice: I’ll go in there and try to convince her otherwise. Fred: Don’t waste your breath. I already tried it. • Sally: No, I won’t agree! Don’t waste your breath. Bill: Aw, come on. At least hear me out.
McGrawhill's American Idioms And Phrasal Verbs