Smart-mouthed refers to a person who speaks in a rude, sarcastic or disrespectful manner. The opposite of smart-mouthed is someone who is polite, respectful, and well-mannered. Other antonyms for smart-mouthed include courteous, cordial, kind, respectful, pleasant, and considerate. These are all traits that reflect good social etiquette and respect for others. A person who is not smart-mouthed is likely to be liked by others, as they are easy to communicate with and don't offend others with their words. In short, being smart-mouthed is not appreciated in society, and it is always better to adopt a polite and respectful attitude towards others.