On a less objective angle... An American (From the country America. Yes, while it can technically be used to describe those on the continents on the western hemisphere, no one else uses the term, therefore, it is fair to say) is someone who supports their country.
And no, that does not mean agreeing with everything the government says or does (It's doubtable that any average citizen around the world agrees with their government completely) but to call one's self a citizen of a country, commiting acts of treason make such a statement questionable.
While the United States is lenient on letting its people badmouth and wish for their country's loss, demoralizing the troops who are working so hard for their country and to liberate the innocent people of the Middle East, it is hard to call someone an American when that person is embarrassed to even be part of The U.S.
No, being patriotic is not being prejudice (Although, I personally believe that everyone is prejudiced in one way or another, such as 'my mother is better than yours'). By definition, it is the pride in one's country. If you hate your country so much, instead of rant about it, why not do something, or better yet, leave. But I digress.
Sorry to say this, but it's just not good enough to have legal papers to be a citizen of a country. At least have some sense of loyalty, eh? Like, I don't know... not making Iraq another Vietnam where we lose because of loss of support of the people and thousands of civilians died.
"But... you said you're an American."
"I am! I was born here!"
"But you want your country to fail and destroy the livelihoods of you and your countrymen?"
"Because George Bush sucks and we deserve it!"
"Then go to Venezuela and support Hugo Chavez and so South America can be united under one dicator..."