"A teacher, eh?" the man in the tuxedo guffaws.
His wife smiles conspiratorially: "No wonder he looks so tired."
The room erupts in laughter. "I laugh, too," Mark Grist says, as the camera moves in for a close-up. "Because she's right - I am pretty tired."
His full reply to the woman's statement forms the basis for a new three-minute film, A Teacher, Eh? Crowdfunded by a campaign that raised more than pound;8,000, the film is a quick-witted, heart-warming and poetic riposte to everyone who fails to understand why a person might want to go into teaching.
Mr Grist is best known as the English teacher who vanquished teenage rapper Blizzard in a rap battle that became a viral hit on YouTube. Viewed more than 4.5 million times, the video shows Mr Grist delivering a relentless volley of rapid-fire rhyming insults.
But Mr Grist's career as a performance poet has also included a stint as poet laureate of Peterborough. In that role, he was regularly invited to formal dinners and town hall events.
"A lot of these people were very scathing of teenagers," he told TES. "I don't think they thought they were being offensive or rude - I think they thought they were supporting me. But they seemed to have a knee-jerk reaction: teenagers are awful and that must be dreadful for you."
A Teacher, Eh? addresses this assumption. Yes, Mr Grist's character acknowledges, he is tired: "Exams get me stressed; giving detentions can be draining. And who'd have guessed it'd be so tiring making lessons entertaining?"
But then he goes on: "I'm tired of asking questions until I realise maybe I don't have all the answers." He is tired, too, of "scrabbling at those locks, dredging back those pearls". But mostly he is tired because he has stayed up all night, trying to answer the probing questions his pupils ask about morality and the world they are growing up in.
"Teaching is a tiring and stressful job," Mr Grist told TES. "But I don't think that's to do with the students. They're one of the good things.
"The best thing about teaching is that you get to work with young people who haven't made up their mind about everything. Maybe you then realise that you've made up your mind about things and that's not necessarily a good thing."
Scenes from the video were filmed at Haverstock School in North London, and the fictional teenagers were played by the school's real-life pupils.
"What he's portraying is exactly how teachers feel," said Nikki Haydon, the school's former assistant headteacher, who is now responsible for community partnerships. "That gut feeling you have: that's why I'm in the job."
Mr Grist's film, she said, accurately portrayed what it was like to be worn down not by teenagers themselves, but by the public's attitude to them. "Teachers do what they do because they believe in it," she argued. "But there are people outside who don't understand the feelings of teachers and how much they're putting into their work and what they want for young people."
Oliver James, 16, who appears in the film as a struggling pupil who suddenly understands a topic, said: "Despite the teacher in the film being fed up with the kids, he still sticks up for them. He feels that, if the kids are not very well-behaved, he still sees potential."
Oliver's classmate, James John, 15, spent "half an hour having paint thrown at my face" in order to play the part of an aspiring artist. "Older people always see young people as troublemakers - criminals, even," he said. "But I think we do care about things as much as anyone else. This is our world as much as anyone else's."
Grist to the mill
Extracts from A Teacher, Eh? by Mark Grist:
I'm tired from days spent saying "tuck in that shirt".
From getting kids into lines, making girls unroll their skirts.
I'm tired of setting tests, the grumbling, the complaining.
Exams get me stressed; giving detentions can be draining.
And who'd have guessed it'd be so tiring making lessons entertaining?
You may be all successful; this meal may well be Michelin.
But I'd swap the swine around me now for a dozen kids on Ritalin.
Teaching is what I do; I feed others before I feed myself,
So that, fingers crossed, I never become as overfed as you.