blueberry pie, n. — Green’s Dictionary of Slang

blueberry pie n.

[the blue uniform + something one can eat v. (4)]

(US gay) a sailor.

1965		Guild Dict. Homosexual Terms 22: homosexual (n.): One with a sexual attraction for those of the same sex who practices sex exclusively with those of the same sex. Related terms: [...] blueberry pie.
1972		B. Rodgers Queens’ Vernacular.
1988		H. Max Gay (S)language.