There is a different set of etiquette here than what we have in the US. For instance, when you walk into a store, it is pretty much imperative for you to greet the store owner with "Bonjour Madame/Monsieur" before you just go about your business. If you forget to do this, they will be displeased with you, and it will show. If you follow this rule, the whole trip will be much easier.
Take, for instance, the Snooty, Rude Waiter, a Parisian stereotype. In America, a bad waiter is one who does not come around often enough to check on you, who makes you wait too long to get the bill, etc. Essentially, one who ignores you. Here, however, checking on you too often, and bringing the bill too soon is considered rude; it would be like rushing you to finish and get the hell out. You wait, not because they are incompetent, but because they want you to have time to enjoy your meal ("deguster" is the word for savoring food). Consider on top of that that the average American probably does not greet the waiter the way it is done here, and just launches into a tirade of orders (probably in English) spoken a bit louder than the acceptable level in Paris (we do speak loudly, I admit), and the entire experience is ill-fated from there.
Of course, stereotypes come from somewhere, and in 2007 the tourism department in Paris launched a campaign called "Paris est vous," distributing leaflets encouraging citizens (and tourists) to be more polite, and giving friendliness and hygiene workshops to local taxi drivers. Maybe I am experiencing the wake of this campaign and am not getting the worst of it. In fact, the Japanese embassy reported that in 2006, 12 Japanese tourists suffered from what they call "Paris Syndrome," when excessively-polite Japanese (mostly women in their mid-30s) come to Paris with very high expectations for what might just be their first trip abroad, and are so thrown off by the rudeness of the locals in their "dream city" that they experience a nervous breakdown, and must be deported back to Japan immediately with medical staff to take care of them on the trip. So maybe I'm wrong.
All in all, though, the basic Golden Rule we all learned in elementary school still stands, it just needs a little cultural education to help out.
PS - from the brochure for Parisians and for Tourists:
"The charter of committments for Parisians reads:
• I will take the time to give information to visitors.
• I will make use of my foreign-language skills to reply to them in their language.
• I will recommend to visitors things I appreciate about Paris.
• I am proud of my city, the No 1 tourist destination in the world.
And the commitments for the visitor are:
• I will experience the Parisian lifestyle.
• I will take advantage of my stay to try French products.
• I will respect the city and use public transport."