Cheese fallen off your cracker?

[Michael Quinion]

Instances provided by Jonathan Lighter:

> He's not running on all 8 cylinders.
> Doesn't have both oars in the water.
> Few cans shy of a six pack!
> Few bytes short of a K.
> He's a couple of sandwiches short of a picnic.
> His elevator doesn't quite reach the top floor.

[etc]

Is there a special name for this kind of comparison that implies a
deficiency in intellect? I ask because Radio 5 Live, a BBC station,
rang me on Monday asking me to do a piece about what they were called
and where they came from (I declined, with thanks, having nothing to
say). The proposed item was provoked by a refurbished post office
which on reopening was found to lack anywhere to despatch letters and
which was therefore described as being "one letter box short of a
post office".

--
Michael Quinion
Editor, World Wide Words
E-mail: <wordseditor at worldwidewords.org>
Web: <http://www.worldwidewords.org/>