Green’s Dictionary of Slang

1. (Aus.) a scrounger.

1912		Sport (Adelaide) 3 Aug. 14/1: They Say [...] Why do the three hummers ride home in Unker’s cart? To save the tram fares .
1919		C.H. Thorp Handful of Ausseys 52: The Independent Order of Hummers and Bummers: Their motto was: ‘Never buy anything nor give anything’.
1919		W.H. Downing Digger Dialects 29: hummer—A Cadger.
1941		Baker Popular Dict. Aus. Sl. 108: Hummer, poler and bot-fly are additional synonyms for a cadger.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 104: The Scholar had long ago hocked his lighter and had since then developed into a compulsive hummer of lights.

2. (US campus) a stupid or inconsequential person.

1969

Current Sl. III:4 7: Hummer, n. An idiot; a backward person.