As a "Limey" I've often wondered how you people saw the term "Yanks" as used during WW2 in the UK and up to to-day? Is/was it ok.
Colin.
Colin and all our British friends,
As an American, I have never taken offense at the term "Yank". That's what I am and I am proud of it. However, let me take your education a little further in this regard.
To a person born in the American south such as I was, a "Yank" can also mean one who is born north of the Mason-Dixon line (the old geographic map line drawn by Congress to separate the then slave-owning states from the non-slave owning states.) Then there is the term, "Yankee". A "Yankee" to a southerner is definitely someone born north of the Mason-Dixon line, of non-Confederate origins, and, until at least World War I, was someone considered of nefarious origins and/or background. This suspicion and distrust of "Yankees" might have been dispelled sooner had the Spanish-American War lasted longer than it did; as it was, WWI broke the ice further and WWII took it even further because by that time it was pretty well agreed that no matter whether you were born north or south of the Mason-Dixon Line, no one was inclined to take up German as the mother tongue.
I mention the terms "Yank" and "Yankee" because my husband is Canadian and try as I might, I don't seem to be able to adequately explain to him what the difference is since he, too, grew up thinking of all Americans as "Yanks". When he really wants to rattle my cage, he'll say something like, "Stick it to the Yanks!" That, of course, never fails to earn him a concussion. 
Marilyn