When I first heard that phrase, sometime in the late 1950s, it was attributed to Ogden Nash. It made sense. He often wrote very short pithy poems.
Apparently there is no basis in fact for attributing that particular bit to Ogden Nash. I've seen it credited to sources in 1965 and 1974, years after I first heard it.
Anybody know for sure of its first use? Who said (or wrote) it?
A quick search found an archived discussion on wikipedia saying:
"... probably popularized in 1964 by Gael Greene's provocative paperback exposé Sex and the College Girl. Presumably she didn't write the line, but only reported it. Google apparently has nothing on the phrase prior to Greene's book."
There was also a published paper in the journal Criminal Law and Philosophy, vol. 7, pp43-59 (2012) titled "Vice Is Nice but Incest Is Best: The Problem of a Moral Taboo". I didn't pull a copy of the full paper, but it's possible (though unlikely) that the author might have researched the phrase's origin.
The similar quote, "A man should try everything once, except incest and morris dancing," was from Dr. Samuel Johnson, best known for compiling the first significant dictionary of the English language.