America is a continent. The people of that continent are Americans, just as the people of Africa are Africans and the people of Europe are Europeans. 

In the United States, once a year, people get drunk to celebrate being Irish. On another day, people put on leather shorts and get drunk to celebrate being German. On other days, people celebrate being Polish, or Scottish, or Russian, or Estonian, or whatever-the-hell-else-they-are.

Then, some Americans cross a border from one part of America to another… and the people get angry and shout, “GET OUT, YOU’RE NOT AMERICAN!”.

Seriously, you people are weird.