waste your breath

waste (one's) breath

To talk of, discuss, or say 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 wasted my breath trying to pitch my idea to the board of directors.
See also: breath, waste

waste your breath

talk or give advice without effect.
See also: breath, waste

waste your ˈbreath (on somebody/something)

speak to somebody or about somebody/something but not have any effect: Don’t waste your breath on her. She doesn’t take advice from anybody.I feel like I’m just wasting my breath trying to explain things to him.
See also: breath, waste