"Sir, have you heard the one about Lauren? She had sex with a boy on top of a caravan."
"It's a wonder it could take the weight," was my quick response.
It was meant to be light-hearted, designed to move the conversation on. I really don't need to know what Lauren was doing at the weekend and I don't need to talk about such things in the middle of break duty.
Was it true? Did I need to waste time finding out? Was it just a way of having a go at Lauren?
Such rumours appear as if from nowhere, lighting up the dark sky like a shooting star, before instantly disappearing. So deflect it and move on. Don't, as they say, give the rumour the oxygen of publicity. My words were a big shock, there was outrage among the girls.
"You can't say that, you are saying she is fat and that's wrong, that is."
Suddenly I am in the middle of a maelstrom. When Lauren arrives the girls are quick to tell her what I said. Now she is in tears in the middle of the hall. The issue is no longer about drunken behaviour, it is about a personal insult.
I have a group of girls gathered around a sobbing Lauren in what they regard as a supportive huddle. Of course they are rather enjoying the drama, pleased that it isn't them.
I have committed one of the worst crimes of all, never mind the rest. I made a comment about her weight. Soon the mobile phones are going off and I have the mother on the line. Lauren has run home.
"I know she was messin' about on a caravan but that's no reason for telling her she is fat," she says.
What does messing about mean, I wonder? I have entered a mad alternative universe where Lauren's behaviour is less important than a flippant comment.
It was time to bring a bit of order to this crazy world. I ask her how much she knows. I suggest that she has a serious word with Lauren. Perhaps you need to offer her some advice? Is there any help you might need in doing this? Would it be appropriate to consult with the family doctor?
When we have restored some sense to all this, the truth slowly emerges. How could I possibly make such a judgment about the safety of the caravan? I couldn't know the combined weight of the two lovers.
But then, as it turns out, neither could Lauren. It was dark and she didn't have a clue who he was.
John Sutton is a pseudonym. He teaches in North Wales