USian.
I am many things: a Hoosier, a Disabled Combat Veteran, an American. But my license plates don't read "Disabled USian Veteran", they read "Disabled American Veteran". As an American and a Veteran, I find this insulting. I'm not saying it's meant to be insulting, far from it. I think most (if not all) of the posters who use the term (The Transatlantic Knowledge Thread is one example) are using it respectfully. Other Americans, other Veterans, might not mind it at all. I do. I get defensive, and unfortunately (and unfairly) affects my view of what the poster has to say.