Researchers from the Kinsey Institute at Indiana University asked a representative sample of 486 18- to 96-year-olds what the term meant to them.
Like Clinton, 30 percent reckoned oral sex didn't count. Nor did anal sex, according to a fifth of the respondents.
What's really bugging us, though, is what was going on with the five percent who said that penile-vaginal intercourse did not constitute sex - a proportion that rose to nearly a quarter - yes, a quarter - in the oldest group of men, in fact.
What does count as sex, for goodness' sake? Have they discovered some wonderful activity that the rest of us don't know about, and which is all that counts to them as the real thing?
There is a serious point to the study. Kinsey research associate Brandon Hill points out that it's common for a doctor, when seeing a patient with symptoms of sexually transmitted infections, to ask how many sexual partners the patient has or has had.
"Researchers, doctors, parents, sex educators should all be very careful and not assume that their own definition of sex is shared by the person they're talking to, be it a patient, a student, a child or study participant," says Hill.