Green’s Dictionary of Slang

1. (US) the head.

1920

Ade Hand-made Fables 69: [They] still have the Idea firmly set in their Cokes that running a Whizzer or whooping before the Draw is a legitimate Pastime.

2. in fig. use, an eccentric, a fool.

1937

D. Fuchs Low Company 77: You must be a coke [...] it’s bad luck busting mirrors.