Green’s Dictionary of Slang

1. (UK Und.) skilful.

1956

R.T. Hopkins Banker Tells All 44: She was Bonzo at putting down. Never a let-up during the whole time she worked for me.

2. eccentric, crazy.

1981

J. Wambaugh Glitter Dome (1982) 80: The fact was that someone was trying to drive Captain Woofer bonzo.