One culture shock aspect you may encounter if you actually get to know a French person might be the expectation of communal sharing. It is seen as basic manners to them, but may seem socialist or even communist to Americans.
To avoid looking selfish or rude, I have listed a few situations below with suggestions. Big surprise, they usually involve food.
l'Apéro (l'apéritif) : The cocktail before the meal.
If you are poured a drink, you may not take even a sip unless everyone else who is having any has been served, and everyone who might possible want to have some has been offered.
Drink slowly and purposefully, since you'll probably only get served 12 ounces of beer every 20 minutes or so. If you feel like re-filling your own cup, be sure to offer everyone else a refill first. The aim is never to get drunk, but only happily tipsy. Acceptable drink choices for the apéro are: Ricard, Martini (the vermouth), Champagne, Port, wiskey, coke, juice, water, or other mixed drink. Not acceptable are wine, liquers like cognac, coffee, tea, or milk.
If food is served it will either be snacks like potato chips, olives, peanuts, pistachios, only help yourself after the host has finished putting out all the hors-d'oeuvres and pouring all the drinks. Savor each chip/peanut/olive, since only a handful is served for the whole table, and never take the last one.
Mealtime:
If you feel that grumble of hunger that means it's time to eat, don't even think about snacking. You must wait until everyone else who might also eat this evening is ready for dinner, and dinner is ready. Sometimes you may need to wait an hour or more, but if you're really starving, you can have apéro (see above). You must sit down together at the same table and share whatever is cooked by putting equal portions on each plate. If someone is allergic to a certain food, or really, really hates it, they may have a separate option, but otherwise each person does not choose what they individually want to eat for dinner. Sharing the same food and eating every bite is part of the ritual that says we are family and community. Even when people are fighting or bored, busy or hours late to dinner, they still sit together, even if they're not speaking to eachother. Food, and time, must be shared. If you run out of water, wine or bread and would like more, be sure to offer to everyone else first, cutting up more bread if necessary. Whoever is serving the dinner must actually serve, doleing out portions and fetching seconds, offering the next course and making sure the coffee is ready at the end.
Snacks:
The few times snacks do happen in France, they're usually in private. You'll almost never see a French person eating in public, never while walking, never on the train, never even waiting for the train. If they are scarfing down a cookie in the metro station, chances are they're not French. Eating in front of others without offering is seen as rude, even when they're complete strangers, so nobody eats in public. A park bench at lunchtime is different, since you're not sitting accross from someone on a train, but almost always, the French will buy a small snack and then wait until they're at home or at their desk to have a bite. If anyone else is around, you must have enough snacks to share equally, even if the other person didn't ask, or doesn't seem hungry.
Birthday parties:
gifts are communal too. While there's nothing wrong with buying a personal gift to give from you to the birthday person, you may find that everyone else at the party has chipped in for one big gift: tickets to a show or a new camera for the birthday person.
Cleaning: paradox of formality vs. familiarity
When you're close family or friends, you might be expected to help set up or clear up after an event. Bring chairs, set the table, wash the dishes, sweep the floor, take out the garbage. If the host is working hard, you should go to help. Although, when at the table, someone else usually does the actual serving of food.
Evenings out:
Why go out with just two of your friends when you can invite everybody? While this does lead to some fun evenings with the group, it can also get tiring and prevent really getting to know any of them more personally. Still, failing to invite anyone may lead them to feel excluded or snubbed.
Live together, eat together, party together. While it took some getting used to, it is nice to feel that there's always people who'll be there for you.
