I am sure this will stir up a hornet's nest but the fact is Charlie, the American tourist is generally not well thought of the world over, I would guess in particular in non-English speaking countries. That is not to say every country doesn't have its own a**holes tourist in someone else's country. I think it's the American tourist's treatment of service staff and country comparisons where it stems from.
Some years ago I was learning Italian so I could travel through Italy for a month - I thought it would be polite to have at least a smattering of their (beautiful) language - our teacher said that when we get their we were to slip in asap that we were from Australia as Americans were not well liked as tourist. I saw why first hand in two restaurants, on a train and at The Colosseum...I still cringe, it wasn't a case of (just) being loud and obnoxious it was the general insulting of the country they were in or (as you said) saying how better it was back home...
I have only been to USA the once, for about two weeks and I never ever met a rude American, in fact I was simply blown away how warm and friendly everyone we met was...had a great time, can't wait to go back. I guess you get out of a country what you put into in to it while there.