From Longman Dictionary of Contemporary Englishwaste your breathwaste your breathspokenPOINTLESS to say something that has no effect Don’t try to reason with Paul – you’re wasting your breath. → waste
Examples from the Corpus
waste your breath• Besides, something told her she'd be wasting her breath.• I ain going waste my breath.• I figure why waste my breath.• You know it and so do I. So don't waste your breath!• Was there any point in even wasting her breath trying to convince him? 