The class was in that preparatory phase, when most have gathered but official business has not yet begun. The question came out of nowhere: "Are you gay?"
Pause for thought. "I'm not sure that's an appropriate question."
He was not to be deflected so easily. "You're a liberal person, aren't you? Surely everything should be up for discussion. No taboos. If you are gay, why should you hide it? If not, same deal."
"I still don't think it's an appropriate question."
"So you are gay then? If not, you'd say you weren't." This from another source, a female student who'd just twigged that something of interest might be going on.
"That's the problem," I said. "Even if you don't answer, it's assumed that you have. Whatever your reaction, someone will put an interpretation on it."
I could see this one wasn't going to go away. With younger students I might have refused to be drawn in right at the beginning. But these were adults, mostly in their early twenties.
As all ears were now tuned in to the discussion, I decided to turn it back on them. "Why might it be wrong for me to be asked such a question?"
Silence. "OK, let's switch it around. If I had asked a student in class the same question, would that be right?"
Consternation. Indignation. No, no, no. "So why is it wrong?"
Another pause, then a variety of responses. It wouldn't be fair. It might be embarrassing. It should be up to them if they want to talk about it. They could be bullied, persecuted, shunned.
"And," I added, "wouldn't it be an abuse of my power if I put a student on the spot like that?" Agreement all round.
"So wouldn't all those things you've just raised apply equally to a teacher? Don't they have rights to privacy?
And you must have heard about students who make life miserable for teachers they suspect of being gay?"
Reluctant acquiescence. Clearly it was a new thought for some: that teachers might have feelings and rights. But we couldn't keep entirely off the personal.
"I've just remembered," said one, "that you've talked about having children."
"And what does that prove?" Having walked so far across thin ice, I thought I might as well walk a little further.
"Haven't you ever come across cases of people who have lived as heterosexuals for a long time, but decide to come out in later life?"
"So you . ?"
"We agreed it's not about me."
"My friend's mum went off with a woman," said someone. "She was 45."
There followed a brief discussion about the morality of this. Plus amazement that people might still have sexual inclinations at such an age.
At this point, I felt the need to draw a diagram. "Surely it reminds us that sexual preference is a continuum rather than just a case of polar opposites?" I said.
While they puzzled over the vocabulary, I drew a horizontal line on the whiteboard, scribing Hetero at one end and Homo at the other.
"Some people," I suggested, "live permanently at one end or other of the railway line. But many others will be stationed somewhere in between."
"And some like to call in at different stations at different times," said the friend of the lesbian mother's daughter.
"And some," said a young man determined to extend the metaphor, "don't live on the main line at all. Their stations are at the end of branch lines."
"True," I said. And then I remembered we had a syllabus to cover. The board rubber did its discussion-ending work.
As Bob Dylan once sang: "I'm liberal, but to a degree."