Both my Random House and American Heritage dictionaries give the Girl Scout point system the credit for the phrase.
Reality Chuck: the fact the that first written citation is from the 1960s doesn’t necessarily invalidate an earlier origin. A large number of words exist in the oral vocabulary before a written cite becomes available. I don’t say this is necessarily the case here, but a WWII origin is not impossible.
Aha, on preview I see samclem’s post. Score one for wordorigins.