Whoever they are everyone in the office is all over them and can't wait to talk to them and changing the way they speak in order to seem a bit cooler and wise to the ways of the USA.

It's just an american. Other nationalities do not get this weird reaction.

EDIT. I am partly guilty of this as the current chap in the office says to me 'what's up brother' instead of hello.

How exciting it's like a movie maybe I shall high five him or do a elaborate handshake or something.