Green’s Dictionary of Slang

1. (US) an amusing person, a fool.

1914		H. Hershfield Abie the Agent 6 Apr. [synd. cartoon strip] Y’ crab-faced gazooni.
1917		Amer. Hatter 46 73/2: The man who thinks he can keep doing his best without the help of other minds is a misguided gazoony.
1923		Wodehouse Leave it to Psmith (1993) 514: You dish-faced gazooni!
1926		J. Stevens Brawny-man 21: Hang on to what you got, gazoony. Pork chops’ll hang high this winter.
1940		‘Argot of the Sea’ in AS XV:4 Dec. 451/1: gazooney. An ignoramus.
1986		R. Campbell In La-La Land We Trust (1999) 17: Oh, for Christ’s sake [...] this gazoony was going to talk like the character in the show.
1995		R. Campbell Wizard of La-La Land (1999) 120: Figuring it would impress this gazooney more than a verbal introduction.
1995		J. Stahl Permanent Midnight 348: You are what the guys on the yard used to call a real gazoonie.

2. in carnival use, a day labourer who usually fails to manage the work and leaves very quickly.

2012

W. Keyser ‘Carny Lingo’ in http://goodmagic.com 🌐 Gazoonie [...] itinerant day laborers who come and go at the drop of a hat. Also [...] a very young and inexperienced worker who probably won't be able to take the hard work and will be gone in a few days.