Green’s Dictionary of Slang

...short of... adj.

also ...shy of...
[var. on not all there adj.]

[1980s+] in combs., a phr. used to mean that someone is unstable or not very intelligent; in specified phrs. below but also in ad hoc combs.

In phrases

couple of chips short of... (also …a computer, ...a cookie, ...an order, couple of computer chips short of a complete circuit, few chips short (of a casino bet), several chips short of a butty, three chips short of a happy meal)

[1990s+] not very intelligent.

couple of tinnies short of a slab (also couple of tinnies short of a six pack) [tinnie n. (1) + slab n. (12)]

[1990s+] (Aus.) eccentric, foolish, simple-minded.

few bob short of the pound (also only eighteen bob in the pound)

[1960s+] unintelligent, eccentric.

few snags short of a barbie (also chop short of a barbie, couple of snags short of a barbie, few snags short at the barbie, …of a barbeque, one sausage short...) [snag, a sausage ]

[1980s+] (Aus.) eccentric, crazy.

few spring rolls short of a banquet (also few french fries short of a happy meal)

[1990s+] unintelligent, eccentric, mad.

ha’penny/ninepence short of a shilling

see under shilling n.

one brick short of a load (also brick short of a load, couple of bricks short of a load, few bricks short of a load, one brick shy of a load, two bricks shy of a load)

[1970s+] slightly insane, eccentric.

one sandwich short of a picnic (also half a sandwich short of a picnic..., pork pie..., sandwich…, sarnie…, two biscuits…, two sandwiches…)

[1960s+] not very intelligent, slightly eccentric, odd.

one sausage short of a barbecue

[1990s+] (US teen) not very intelligent, slightly eccentric, odd.

one stop short of East Ham (also one stop from Barking) [pun on London Underground stop Barking / barking adj.]

[1990s+] mad, eccentric.

twopence halfpenny short of the deener [deener n. (1)]

not wholly sane.

two pence short of a bob [a bob n.3 (2) was composed of 12 pence]

[20C+] not very intelligent, slightly eccentric, odd.

two tacos short of a combination plate

[1980s] (US) not very intelligent, slightly eccentric, odd.

two wafers short of a communion (also couple of...)

[1960s+] not very intelligent, slightly eccentric, odd.