As an Australian in America, I have never encountered anti-Australian prejudice. I don’t know many Brits who’ve encountered anti-British sentiment in America.
But if you go to Australia or the United Kingdom or Europe, you’ll find about a third of people have a huge anti-American chip on their shoulder.
I think this hatred is very similar to Jew hatred. People resent Jews for what they represent — the call to a higher moral law. People resent Americans because the United States of America is the one country — aside from Israel — that stands for a universal value system.