"There is nothing... (poem)" joke

Found Parable by J.D. McClatchy (published in the 15 November 1993 issue of the New Yorker, p. 72)
In the men's room at the office today
some wag has labelled the two stalls
the Erotic and the Political.
The second seems suitable for the results
of my business, not for what thinking
ordinarily accompanies it.
So I've locked myself into the first because,
though farther from the light bulb overhead,
it remains the more conventional
and thereby illuminating choice.
The on its walls is more desperate.
As if I had written them
there myself, but only because by now
I have seen them day after day,
I know each boast, each plea,
the runty widower's resentments,
the phone number for good head.
Today's fresh drawing:
a woman's torso, neck to outflung knees,
with breasts like targets and at her crotch
red felt-tip "hair" to guard
a treasure half would, half wisecrack.
The first critic of desire is always
the self-possessed sensualist.
With all that wall as his margin,
he had sniffed in smug ballpoint
OBVIOUSLY DONE BY SOMEONE
WHO HAS NEVER SEEN THE REAL THING.
Under that, in a later hand,
the local pinstripe aesthete
had dismissed the daydreamer's crudity
and its critic's edgy literalism.
His block letters had squared,
not sloping, shoulders: NO,
BY SOMEONE WHO JUST CAN'T DRAW.
Were the two opinions
converging on the same moral point?
That a good drawing is the real thing?
Or that the real thing
can be truly seen only through another's
eyes? But now that I trace it through
other jokes and members,
the bottom line leads to a higher inch
of free space on the partition-
a perch above the loose
remarks, like the pimp's doorway
or the Zen master's cliff-face ledge.
THERE ARE NO REAL THINGS
writes the philosopher. But he, too,
has been misled by everything
the mind makes of a body.
When the torso is fleshed out
and turns over in the artist's bed,
when the sensualist sobs over her,
when the critic button's his pants,
when the philosopher's scorn sinks back
from a gratified ecstasy,
then it will be clear to each
in his own way. There is nothing
we cannot possibly not know.