ArishMell · 70-79, M
One .... short of a ...
Insert objects of choice, e.g. "card" and "pack". I've heard all sorts of versions!
Similarly,
Not the brightest bunny in the burrow.
There are many versions of this, too.
If Xxxx had brains he/she would be dangerous.
Xxxx left [this club] and joined [that club], raising the average intelligence of both clubs.
This is used in friendly rivalry between amateur sports clubs and similar.
No brighter than he/she should be.
That is particularly a Northern English judgement, and uses "better" instead of "brighter" when criticising the person's behaviour rather than intelligence.