Wordorigins.org

This term derives from the girl scouts. That organization had (has?) a system of points that the girls would accumulate toward advancement.

The phrase entered the general language from WWII in military slang. Uniforms, the army’s tendency to have soldiers do things that seemed silly and child-like, and evocation of brown-nose all contributed to the popularity of the phrase.

(Source: Historical Dictionary of American Slang)