The phrase "giving a piece of one's mind" means expressing one's opinions, often in a harsh or critical manner. Its antonyms, on the other hand, involve being reserved, cautious, and withholding one's opinions. These antonyms include words like diplomacy, tactfulness, and consideration. One can choose to communicate their thoughts in a more empathetic and calm manner, using phrases such as "I understand your perspective, but..." or "I see where you're coming from, however..." This approach helps to avoid conflict and promotes mutual understanding. Therefore, instead of giving a piece of one's mind, one can practice being tactful and diplomatic in their communication.