Walter (Mitty), n. — Green’s Dictionary of Slang

Walter (Mitty) n.

[rhy. sl. = titty n. (1); ult. Walter Mitty, fictional character created by James Thurber]

(Aus.) the female breast.

1983		J. Byrell (con. 1959) Up the Cross 14: Brenda [...] had been blessed with just about the sweetest and firmest and plumpest set of walter mittys this side of Fremantle.
2003		B. Dark Dirty Cockney Rhy. Sl. 105: I spend my whole life dreaming about Walters.