Dining etiquette in France
As a rule, the French don't have much tolerance for picky eaters. While it's fairly common to customise an order of food according to one’s preferences in foreign restaurants, this behaviour isn't acceptable in most French establishments or at someone’s home.
Once the usual questions around food allergies have been addressed, the host/hostess expects guests to finish what they're served. It is frowned upon to leave food on a plate, especially as servings aren't typically large and food preparation, particularly in someone’s home, is a labour of love that can only be reciprocated through appreciation and enjoyment of the meal.
The same appreciation for good food extends to office canteens and school lunches. Many French schools offer school lunches in the form of three-course meals from entrée to cheese or dessert after the meal. This is also the case in office canteens.