Green’s Dictionary of Slang

gay n.2

[galah n. or jay n.1 (4)]

(Aus.) a dupe, a sucker, a gullible person.

[Aus] in K. Tennant Foveaux in DSUE (1984).
[Aus]Baker Aus. Lang.
[Aus] ‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxv 6/1: gay: A not very smart person who would be if he could be.