These days I try not to admit in public to being a teacher, preferring to be thought of as something more respectable, like a pimp, a loan shark or an international arms dealer. So that was my first mistake. My second was rising to the bait.
"Oh," he said, peering over the top of his glasses as if at a biological specimen, "you teach in a college, do you? That sounds like a soft number."
He was called Eric. Or maybe it was Derek. Dickhead was the handle that first came to mind but I don't suppose it said that on his birth certificate. We had been thrown together at a social function, finding ourselves stranded on the margins with only each other to talk to.
Eric revealed that he worked in sales. He was sure teaching was a doddle compared with this. "I hear teachers moaning and complaining about their visits from Ofsted," he said, "but honestly, Stephen, you lot need to get real. Once every few years, a couple of inspectors wander into your classroom and that's it. In sales, we're monitored all the time. The bottom line, that's all that matters. If you sell, you eat. If not, you're history."
And that was all it took. He had lit the blue touchpaper. "Imagine if you can, Eric," I said, "that your very important job in sales is like an iceberg. Only a tenth of it is visible to others. But the rest, hidden away below the surface, is still very real to you.
"So now selling is only a small part of what you actually do. Much of the rest of the time is spent trying to prove to others that you actually are selling things. It's as if you have an imaginary friend following you around, and you must convince him that you are doing your job well.
"All of this, of course, has to be done in writing, in a laborious and detailed format that is just sufficiently different from last year's format to ensure that you have to do the whole thing over again.
"Then there are your plans. These aren't working plans that will actually help you in selling things - don't be so naive, Eric - but extraordinarily detailed plans, stretching ahead for at least a year, which you can show to your manager, who can show them to her manager in case, one day, that manager may have to show them to an inspector."
"But." said Eric. By now I was in full flow, so he had no chance.
"You will, of course, be expected to conduct a forensic review of your own performance at regular intervals - what went right, what went wrong - and write it all down for your imaginary friend, in another hugely complex format dreamed up by someone who might once have been a salesman but only a very long time ago.
"And then." But suddenly we were both aware that the rest of the congregation had gone silent, gathering in a circle around us like children ready for a playground fight. At this point Eric gratefully took the opportunity to slip away.
"Teacher," said one of the onlookers, making that twisty sign with his index finger on his temple that indicates someone has a screw loose. "Ah, yes," said another, "that would explain it."
Stephen Jones is a lecturer at a further education college in London