Green’s Dictionary of Slang

John Bull adj.²

(Aus.) drunk.

1912		Sport (Adelaide) 8 June 14/2: They Say [...] Tommy N. has caught a tart, and turned the shicker [...] down. Tom now takes a drop of Fisherman’s Daughter, and doesn’t get John Bull.
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 90: He reckons you’re a bit John Bull already.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxv 6/3: john bull: Full, inebriated.