Antonyms for the term 'good mannered' refer to the lack of civility and proper behavior. Some antonyms include impolite, rude, discourteous, rough, uncivil, indecorous, boorish, and ill-mannered. These terms describe individuals who are unkempt, use foul language, and have no regard for social norms. Being ill-mannered can lead to a negative image and can affect how people perceive someone. It is important to cultivate good manners to create social harmony and respect in society. A person who is well-mannered shows respect towards others, creates a positive image, and develops healthy relationships.