It means that the way you act seems artificial or exaggerated. Chill out. Manners are the way we behave in society, how we speak and act with other people. Use mannered to say that someone has exaggerated or unnatural manners.

What is the synonym of well-mannered?

affable. considerate. cordial. courteous.

What is the synonym of manner?

Some common synonyms of manner are bearing, carriage, demeanor, deportment, and mien. While all these words mean "the outward manifestation of personality or attitude," manner implies characteristic or customary way of moving and gesturing and addressing others.