Is this the one? From one of the "Bawdy Songs" series.

Four-Letter Words — Oscar Brand

CHORUS (Each stanza)
The four-letter words, the four-letter words,
That never say quite what you mean.
We'd rather be known for our hypocrite ways,
Than vulgar, impure and obscene.

When nature is calling, plain speaking is out,
When ladies, Lord, love 'em, are milling about,
You may wee-wee, make water, or green up the grass,
You may powder your nose, even "johnny" may pass,
Shake the dew off the lily, see a man 'bout a dog,
Or, when everyone's soused, try condensing the fog,
But, please to remember, if you would know bliss,
That, only in Shakespeare, do characters ... ...

Now, a woman has bosoms, a bust or a breast,
Those lily-white swellings that bulge 'neath her vest.
There are towers of ivory, sheaves of new wheat,
In moments of passion, ripe apples to eat.
You may speak of her nipples as fingers of fire,
With hardly a question of raising her ire,
But, by Rabelais' beard, she will throw several fits,
If you speak of them roundly as good honest ... …

Though a lady oppose your advance, she'll be kind,
Just as long as you intimate what's on your mind.
You may tell her you're hungry, that you need to be swung.
You may ask her to see how your etchings are hung.
You may mention the ashes that need to be hauled,
Put a lid on the saucepan, even "lay"'s not too bold,
But the moment you're forthright, be ready to duck,
For the girl isn't born yet, who'll stand for "Let's ... ...

So, let's banish those words that Elizabeth used,
When she was Queen virgin, and itched on her throne.
The modern maid's virtue is easily bruised,
On meeting the four-letter words all alone.
Let your morals be loose as an alderman's vest,
If your language be weaseling, vague and obscure.
Today, not the act, but the word, is the test,
Of the vulgar, salacious, illegal, impure.