The phrase "flap one's tongue" refers to talking excessively or indiscreetly. To express the opposite meaning, we can use antonyms such as "be quiet," "keep silent," "reserve," "hold back," "listen," or "think before you speak." These words indicate a sense of restraint, introspection, and consideration towards others' feelings. In contrast to the negative connotation of flapping one's tongue, these antonyms highlight the importance of active listening, empathy, and self-control in effective communication. Therefore, using these antonyms can promote a more constructive and respectful conversation, avoiding misunderstandings, conflicts, or hurtful comments.