Politeness?

One prevailing opinion that Americans have of French people and French people have of Americans is that They Are Rude.

As far as I can tell, a lot of this is due to cultural misunderstandings.  

Respecting Privacy

Americans don't greet people properly before engaging them in a full-blown conversation.  If you just start talking to a French person in an elevator or somewhere else without greeting them, it is very strange.  This leads to French people feeling confused and annoyed that someone has improperly butted into their private space.  An American may think they are making friendly small-talk, but without a proper greeting, it is an imposition.

Restaurant Server Attention

In the United States, wait staff are underpaid and make up their wages by "earning" tips.  When an American goes to a restaurant, they examine everything their server does and uses it to justify how much they will leave for a tip.   If they waiter is not attentive, does not bring food quickly, does not refill the water, does not act polite, does not smother the diner with attention, etc, then their income can suffer.  In France, meals aren't about promptness, they are about sharing foods with someone and spending time together.  While an American restaurant will have tables turn over many times per evening, a French table may only be used for one seating.  You can gently enjoy your food in a slow-paced manner while talking with your company.  There may be an hour between the end of the meal and when the desert is brought out.  The whole affair will last 2-3 hours.  French waiters are not typically tipped, but rather paid by the restaurant.  Or, in the case of small places, the owner of the restaurant will be bringing you your food.  It is actually quite funny to read American reviews of French restaurants on travel sites.  Most of the critiques are really examples of French waiters giving their customers polite space and time to enjoy their food and company.

Loudness

Stereotype?  Are Americans loud?  I can only speak from experience that every loud tourist that I notice happens to be yelling something in English with an American accent.  When Dan and I visited Venice, there was a table of Americans just across the restaurant from us.  They were oh so loud.  And I, certain people claim, am loud.  The children are always loud.  We are working on being quieter and not yelling things across the road or park at the children, but it is possible that we are loud anyway.  

Sure, sometimes people, whatever their nationality, are rude.  But usually, if you make an effort to be pleasant, people will probably return the effort.

And even if people initially seem rude... keep trying.  Maybe they will be better after 10 minutes.

An attempt at rudeness, but only temporarily