be wasting (one's) breath

be wasting (one's) breath

To be talking of, discussing, or saying things that are likely to be ignored or are in vain. Don't bother trying to change my mind about this, you're wasting your breath! It looks like I was wasting my breath when I tried to pitch my idea to the board of directors.
See also: breath, wasting

be wasting your breath

If someone is wasting their breath, there is no point in them continuing with what they are saying, because it will not have any effect. He wanted to protest again, but the tone of her voice told him he was wasting his breath. Before I could get very far he interrupted me to tell me that I was wasting my breath. Note: You can say that something being said is a waste of breath. He would admit to the thefts, but deny everything else, and her accusations would be a waste of breath.
See also: breath, wasting