Green’s Dictionary of Slang

not very intelligent, slightly eccentric, odd.

1986		R. Beckett Dinkum Aussie Dict. 38: Not the full bottle: Means that someone is ‘not the full quid’.
1998		G. Burn Happy Like Murderers 93: She wasn’t the full cup of tea in her brother Andrew’s opinion.

(Aus.) not very intelligent.

1962

J. McNeill How Does Your Garden Grow? in Dutton Lit. of Aus. (1976) 288: sam They do say, sir, that I’m...ahh, well, they do say that I’m not the full deener.

(US/Aus.) not very intelligent, slightly eccentric, odd.

1863		G.A. Sala Breakfast in Bed 80: ‘Uncle Abe’ had only ninety-nine cents out of the mental dollar.
2002		Wattle Creek Wire No. 16 Fall, at Wattlecreek.com 🌐 People for years have correctly questioned my sanity and when you consider the time line in establishing a winery, you will probably agree with the masses that I am not the full dollar.

see under shilling n.

not up to standards, not as promised or advertised.

1963–74

B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 14: This trip isn’t the full two bob.