We all know that men shall be men (and women shall be women), but in Paris, be a gentleman and a lady. For guys, this means offering your hand to a woman who is getting into or out of a taxi or a car—settle her into her seat, help her in and out of her coat. This can be especially important for business travelers who will be interacting with the opposite sex. Women, especially those of you who are accustomed to making your own way in the world, may need to get used to being waited on a bit.
An abundance of exuberance, which often means boisterous actions and loud voices, may cause discreet Parisians to raise their eyebrows or give a deep chesty sigh. They're not being rude, though they are opting to indicate that they think you are. Be aware of your surroundings and lower your voice accordingly, especially in churches, museums, restaurants, theaters, cinemas and the Métro.