know from

[Douglas G. Wilson]

>Actually, there is one (euphemistic) variant that I must have had in
>the back of my mind when I was (mis)writing earlier: "doesn't know
>his ass from his elbow".  I was thinking of the "doesn't know his ass
>from a hole in the ground", though.  Sorry for the confusion.  (I
>wonder why "elbow" was chosen for the euphemism--as a non-hole, it
>seems as though an elbow would be a lot easier to distinguish from an
>ass, or a hole in the ground.)

The alternative to "ass" is not necessarily a euphemism IMHO. In my
experience it can be almost anything. I remember for example "doesn't know
his ass from page eight" from my school days, the sense [if any] of "p. 8"
entirely opaque to me. Similarly, with similar sense, "couldn't find his
ass with both hands/with a flashlight/with a roadmap/etc." The idea is to
include the rude "ass" somehow, for force/machismo.

"Ass from elbow" I believe is favored by alliteration. There is a
comparable expression "asses [or assholes} and elbows" referring to
dedicated labor: "You swabbies get busy scrubbing that deck; when I come
back, I don't want to see nothing but assholes and elbows!" ... i.e., "I
don't want to see anybody walking around smoking; I want to see everybody
on hands and knees scrubbing" [buttocks and elbows prominent from the rear
view, but "ass(hole)" favored by a desire for rudeness].

-- Doug Wilson