All good points irateplatypus.
But let me add some further comments.
You're right that in most cases, "rude" American tourists are not being rude per se, but are just acting outside the local norms. Talking loudly in public is one example. They don't do it to annoy people, but some people get annoyed because it's considered rude or crass in that society. Ignorance of local customs (short sleeves and trousers in some Mediterannean countries for example). Again, it's not as if they are
trying to annoy anyone.
Having said that, Americans are also used to a friendlier and/or higher level of service. So they are quite often put out by the apparent snotty attitude of waiters, shop assistants etc they meet on their travels. Again, these people are not trying to be rude (for the most part) to the American tourist, but it may appear so to them.
In other words, the vast majority of "conflict" that occurs is due to misunderstanding and differing cultural norms. Having said that, the tourist is the one visiting and it is incumbent upon them to adapt to the local conditions.
How often do you see a German, French or Italian tourist talking loudly in German, French or Italian at an American restaurant and getting frustrated they are not understood?
Mr Mephisto
PS - For the record, I love America and Americans. I think you guys are great. Just keep the voice down a little, and learn a bit about the history/culture of where you visit, ok?