A person who is:
An American From the Northern U.S.
A player for the New York Yankees or a fan of theirs
A person from NYC
A girl who wears a short skirt and has bleached hair (in Japan) Can also be spelled yanki
That @#$%* who works at my school library and guards the bookshelves, saying things like "I'm going to report you kids! How dare you stand and talk by those bookshelves! You are blocking off the other students from getting books!" when there is absolutely NO STUDENT anywhere nearby looking for books (true story.) Will also make sure that no one puts a backpack on a table, and takes a tally of how many students enter the library. Any other librarian who acts in a similar manner.
Man, my school is f***ed up because of that library nazi!