Answer:
Perhaps you are looking for Danse Reusse by William Carlos Williams:
If I when my wife is sleeping
and the baby and Kathleen
are sleeping
and the sun is a flame-white disc
in silken mists
above shining trees,-
if I in my north room
dance naked, grotesquely
before my mirror
waving my shirt round my head
and singing softly to myself:
"I am lonely, lonely.
I was born to be lonely,
I am best so!"
If I admire my arms, my face,
my shoulders, flanks, buttocks
against the yellow drawn shades,-
Who shall say I am not
the happy genius of my household?