It is very unfortunate, but I've run into this general perception
whenever I travelled abroad.
When visiting a foreign country with limited exposure to other cultures, you are automatically at a disadvantage because you do not know the local customs and (usually) the language. When they ask where you are from, if you answer American they automatically assume you are a rich Texas oil baron with the manners of a retarded goat. I had one guy ask where my Ten Gallon Hat was. It saddens me that the Americans that they had met before were, basically, assholes. I had to work at overcoming the stereotype. I didn't wear flashy items to show I was well off. I took the time to learn local customs and as much of their language as I could. When the group I was with passed a group of monks in Thailand and I was the first one to automatically properly perform a wai, they realized that not all Americans are thoughtless jerks.
Actually, while I was in Thailand, the local folks looked down on the Germans the most. Siemens was installing an elevated train system, and they had a lot of German folks there. Of the nine I knew personally, only one treated the Thai people with any respect. There were a bunch of British folks there too, and every one I knew treated the Thai with respect. Needless to say, the Brits and I were invited out all the time, which annoyed the Germans. Perhaps it was the fact that the Germans were in charge of getting things done, and they had a lot of pressure on them.
I ran into this stereotyping in Thailand, Sri Lanka, Singapore, Guangzhou (China), Bahrain, Hong Kong and (surprisingly) in the Phillippines. You get this jokingly in Canada, but it's more like two brothers picking on each other.
All I can say is it is your responsibility to leave a good impression on the local folks you come in contact with. When I was in the Navy, my Commanding Officer said it best:
"Remember, you are Ambassadors for your country. What you do here should be remembered with fondness, not bitterness."
Discounting my government and the things it does, I do my best to let the people I meet on my travels know that not all the folks from the United States are Ugly Americans.