Smiling? It’s just an option
It's a curious message that the Alpes-Maritime tribunal has just sent by compelling a luxury hotel in Cannes to pay over large indemnities to an employee who was fired "without any real cause" when she refused to be kind to customers. So, it seems it is legally possible to be unpleasant to customers. It is not considered misconduct, even when one is the maître d' in a luxury restaurant!