Learn English – Why “short of a six pack” means someone is stupid or missing common sense

slang

One Short of A Six Pack

A term used to describe a person who is not all there. A person
missing a marble or two – a few percentages off from being full blown
retarded.

Another similar slang:

two cans short of a six pack

adj. stupid or crazy; not "all there." oh man, look at this two cans
short of a six pack

But I don't know how the means(missing common sense or stupid) comes froms short of a six pack. So could anyone please give me some hints about that?

Best Answer

In this usage, short means:

5a : not coming up to a measure or requirement : insufficient in short supply
b : not reaching far enough the throw to first was short
c : enduring privation
d : insufficiently supplied short of cash, short on brains
_{source:Merriam-Webster}

Sense D is the most exact match; the idea is that a "normal person" has enough sense or capability to achieve a standard measurement (represented by some arbitrary item, in this case a package of beverage containers that normally has 6 units), but the person being talked about does not have enough sense or capability to achieve that same measurement.

"I was X short" is generally used as a quick way to say "I needed (some number N) of something, but I only had (some smaller number, Y)", then X = N - Y, so if you need $12 to buy something but you only have $11, you are one dollar short.

The expression, then, equates intelligence to beer: you need 6 units (cans) to be normal, but the person being discussed is "one short of a six-pack": they have only 5 units of intelligence, not the 6 expected.