A teenage mother was telling me she had two pregnancies before the age of 15, and I then ventured to ask if there had been any sex education at her school.
"Oh yeah! It was a hoot!" she chortled. "We were all cracking up with laughter while the teacher struggled to pull a condom onto a banana! The lads were making gestures, and you should have seen the teacher's face - she was beetroot with embarrassment!"
It was at that moment that I decided that teaching sex education to adolescents, or pre-adolescents, must be one of the least-envied of professional tasks.
There may be individuals who can deliver such a lesson skilfully, but, it would seem, not very many. An international survey of sex education in schools - involving 10 countries - reported that young people grouched and grumbled about almost every single aspect of sex education lessons.
They said sex education was out of touch and complained it was "gendered" - differentiating between male and female roles. Yet they also reported that, in the classroom, boys often behaved disruptively while girls were slagged off if they seemed to be well acquainted with the subject matter. This indicates that young males and females do indeed react differently, and are indeed "gendered".
They said sex education was "overly biological" and all those biological facts "de-eroticised" the content.
But, look, if a sex education lesson were to be "eroticised", a teacher today might well be accused of "pornification", and might even end up on the sex offenders' register. Exchanging erotic content with young people can be categorised as child sexual abuse.
The young people who took part in this study - they were between the ages of 12 and 18 - did concede that they didn't like their own class teachers to conduct the sex education session: it "blurred" the boundaries. So perhaps they did get the point that erotic content can be an area of some sensitivity.
The teenagers wanted more about homosexuality, although if they sought more info on this, they might read a few biographies about English public school life in the Thirties and Forties. Terence Rattigan, that incomparable playwright, was involved in an active gay relationship with his form teacher at Harrow when he was 16. His biographer reflects that most of the teenage boys at this posh public school had homosexual experience anyway.
Overall, the young people in the current study - carried out at the University of Bristol and published in September by the British Medical Journal - judged that sex education as it is now imparted was just too "negative".
They also said that adults didn't face the fact that adolescents might already be sexually active. Perhaps, as some educationalists believe, sex education should be started much younger: at four or five years of age. As soon as kids can get online, they'll often be able to access sexually explicit material anyway.
But at whatever age this life-lesson will be delivered, my continuing sympathy is with the teacher landed with the task. They will never meet the demanding standards of their charges, since sex education is a devilishly difficult subject to impart in any kind of a balanced way.
This is partly because a classroom lesson is normally a rational procedure - two and two make four: the French Revolution occurred in 1789 - but sexual desire rarely conforms to the norms of rational thought.
Sexual desire may extinguish, temporarily, rational thought.Any progressive teacher who decides to comply with the students' demands to introduce more eroticism into sex lessons may find that among the adolescent boys in her classroom, arousal could well be an immediate factor, in which case you can forget about the brain's input.
The kids may complain about sex lessons being "overly biological", but at least with biology you can concentrate on provable facts. Once you go beyond facts, you are straying into territory heavily weighted with subjective values: a Krafft-Ebing foot-fetishist might impart a very different sex education lesson from an earth-mother, for whom the satisfaction of fertility is intrinsic to the experience.
I agree with one point the teenage complainants make: sex education shouldn't be all negative. It shouldn't over-focus on the dangers of sexually transmitted diseases and unwanted pregnancy. It should indeed talk about joy and pleasure and the happiness that couples can have from erotic love and great relationships. Even if you can't ignore the darker side - sexual relationships can be destructive, exploitative, abusive, cruel, spiteful and manipulative as well - and too much obsession with sex has destroyed individuals and relationships. Restraints and taboos were there for a reason.
But maybe great literature is the way to learn about the deeper meaning of sexual relationships, both in its pleasures and in its consequences. At a basic level, the teacher can only reach for the facts. And even then, she may not manage to get the message across. I asked the teenage mother why, if the teacher had gone to such embarrassing trouble to demonstrate the condom on the banana, she had nonetheless become pregnant at 13? "Dunno," she said. "It just looked so daft, it didn't seem natural."
Poor teacher, indeed.