jkuh

Ah well, the safest explanation when an entire country’s people are stereotyped as rude is that they have their own culture with different criteria for politeness than the ones you are used to. It’s probably easier for Americans to forget this than for the rest of the world, because they consume less foreign media than the rest of us (from literature in translation to foreign films) and are less exposed to aspects of foreign cultures that could inform them about different norms of politeness (online interactions happen in their own language and follow their own (anglo) social codes.) With this insular worldview it's easy to take it for granted that American good manners are universal. They are not!

A very common gripe against American tourists in Paris is that they talk so loudly in public spaces, which is definitely rude here but I assume that in the US, people just have a different threshold for what constitutes 'loud' (I wonder if it is due to being used to having more space than Europeans). I also remember a discussion I had with one of my translation professors about the American concept of ‘active listening’ and how negatively it is perceived in France. It may be that in the US it is polite to make 'listening noises' at regular intervals while someone is speaking to you, ‘uh huh’, ‘right’, ‘yeah’, ‘really?’, and that you would perceive someone who just stands there silently as disinterested or thinking about something else. In France it is more polite to shut up and listen (with the occasional nod or ‘mmh’) and it's rather seen as annoying and rude to make a bunch of useless noise while someone is speaking.

There are of course countless examples like that. The infamous rude waiters in Parisian cafés probably seem a lot more rude and cold to people who have a different food culture... People from other cultures might consider a waiter terrible at his job if he doesn’t frequently check on them to make sure they don’t wait for anything, but the idea that a meal is a pleasant experience rather than just a way to feed yourself (esp when eating out) means we like having time to chat and just enjoy our table for a while, so we don’t mind as much waiting to order or for the next course. French people would typically hate if an overzealous waiter took the initiative to bring the note once we’re done with our meal so we don’t have to wait for it, as it would be interpreted as “you’re done, now get out of my restaurant.”

The level of formality required to be polite is quite high in France, which might contribute to French people being seen as rude by people with a more casual culture. To continue with waiters, even in casual cafés they will address clients with the formal you and conversely, and won’t pretend to be your friend (the fact that we don’t have the American tip culture also means they don’t feel the need to ingratiate themselves to you.) I remember being alarmed when a waitress in New York introduced herself and asked how I was doing. “She’s giving me her first name? What... am I supposed to with it? Use it?” It gave me some insight on why Americans might consider French waiters rude or sullen! It might also be more accepted outside of France to customise your dish—my brother worked as a waiter and often had to say “That won't be possible” about alterations to a dish that he knew wouldn’t fly with the chef, to foreign tourists who were stunned and angry to hear that, and probably brought home a negative opinion of French waiters. In France where the sentiment in most restaurants is more “respect the chef's skill” than “the customer is king”, people are more likely to be apologetic if they ask for alterations (beyond basic stuff) as you can quickly be seen as rude, even by the people you are eating with. 

And I remember reading on a website for learning English that the polite answer to “How are you?” is “I’m fine, thank you!” because it’s rude to burden someone you aren’t close to with your problems. In my corner of the French countryside the polite thing to do is to complain about some minor trouble, because saying everything is going great is perceived negatively, as boasting, and also as a standoffish reply that kind of shuts down the conversation, while grumbling about some problem everyone can relate to will keep it going. (French people love grumbling as a positive bonding activity!)