1. 矫揉造作的;不自然的;做作的
If you describe some-one's behaviour or a work of art as mannered, you dislike it because it is elaborate or formal, and therefore seems false or artificial.

2. 有礼貌的;彬彬有礼的
Mannered behaviour is polite and observes social customs.

1. having unnatural mannerisms

e.g. brief, mannered and unlifelike idiom