The term "give a piece of one's mind" refers to expressing one's thoughts, criticisms or complaints, often in a confrontational or aggressive manner. The antonyms for this phrase would be "holding back," "withholding criticism," or "keeping one's thoughts to oneself." Other antonyms might include "peaceful discussion" or "agreeable exchange," which would involve finding common ground or seeking to understand another's perspective. Alternatively, one might consider using phrases such as "constructive feedback," "positive reinforcement," or "praise" as antonyms, which seek to encourage or motivate positive behavior rather than criticize or confront negativity.