I'm surprised nobody has mentioned the Woody Guthrie song
"Walt Whitman's Niece" - words by Woody (1946) music by Billy Bragg,(1997) from the album Mermaid Avenue:

Last night or the night before that
I won't say which night
A seaman friend of mine
I'll not say which seaman
Walked up to a big old building
I won't say which building
And would not have walked up the stairs
Not to say which stairs
If there had not have been two girls
Leaving out the names of those two girls

I recall a door, a big long room
I'll not tell which room
I remember a deep blue rug
But I can't say which rug
A girl took down a book of poems
not to say which book of poems
And as she read, I laid my head
and I can't tell which head
Down in her lap
and I can't mention which lap

My seaman buddy and girl moved off
After a couple of pages and there I was
All night long, laying and listening
And forgetting the poems
And as well as I could recall
Or my seaman buddy could recollect
My girl had told us that she was a niece
of Walt Whitman, but not which niece

And it takes a night and a girl
and a book of this kind
A long long way to find its way back

Sleeve notes say Woody wrote this in 1946 - pretty explicit for the time, I think! Now just to figure out if it was a twosome, a threesome or a foursome!

Cheers,
Quokka