Green’s Dictionary of Slang

1. crazy, eccentric.

1944

J. Cary Horse’s Mouth (1948) 95: It made me want to go bozo with the old rascal.

2. stupid, with implications of thuggishness.

1989		A. Sorkin A Few Good Men (1990) 55: I don’t want to hear about your bozo code of honor.
1997		N. Barlay Curvy Lovebox 187: A couple of bozo doormen stand with their hands clasped over their little dicks.
1999–2000		Guardian Guide 18 Dec.–3 Jan. 89: Fairly unengaging bozo comedy based around the Mann law of the 20s.