Green’s Dictionary of Slang

coo-coo adj.1

[abbr./redup. of cool adj.]

(US) sophisticated, aware.

[US]‘Lord Buckley’ Hiparama of the Classics 8: They wailed so far out, and so Crazy and so Coo-Coo. [Ibid.] 25: Look at Princess Libadee [...] She look pretty coo-coo today.