A phrase used to disambiguate between
people living in the United States and
people living in the continents of North or South America, since "American" can refer to either group of
people.
When talking to people who have this phrase in their vocabulary, "United Statesian" always refers to only people living in the United States, while "American" always refers to people living anywhere in North or South America.
Jack:
Dude, Americans are so fucking stupid.
José: Wtf
dude
Jack:
Sorry, I meant United Statesians.
José: Oh okay :)