I’ve traveled in more than 50 countries and on all seven continents. Despite what lots of folks believe, foreign citizens DO NOT hate Americans. Many people from other countries really dislike our governmental policies, but they don’t extend that hatred to the average American person who is traveling in their country.
To put things in perspective, think of Cuba. You may disagree with the communist government, but would you treat the average Cuban person badly because of your dislike for communist politics? Most of you would not. It’s the same way when people from other countries meet Americans.
Then why would you want to dress to avoid looking like an American? Mostly it’s because Americans are considered wealthy by third world standards. As an American, you will be targeted by more scams, solicitations, and even robbery attempts. Try to blend in as much as possible when you travel. This article gives you some good starting points.