Green’s Dictionary of Slang

crazy, eccentric.

1921		N&Q 12 Ser. IX 418: An officer whose orders seemed incomprehensible was said to have ‘gone stone-winnick.’.
1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier 179: Winick. — To be or to go winick meant to be mad or foolish.