It was the last full day of a summer holiday that never really took its brakes off, weather-wise, but felt endless and elegiac nevertheless, and the 12-year-old and 13-year-old decided to mark the occasion with a bitter row over how often you should wash your hair. It wouldn’t have made it into their top-ranking fights (in order: who is more spoilt? Does nature contain maths? Can you be a vegetarian except on Fridays? And are dog years a thing, which was resolved, at least to my satisfaction, with the “there is no Dog Sun, therefore there is no Dog Year” line from TJ, the older one, even though I still agree with H that the dog is 35. I find the Solomon role tiring and decline to perform it).

However, this might yet be their longest argument, stretching from when they woke up, all the way through two baths, which may or may not have involved shampoo, right up to the early evening when I dropped them at their dad’s house. “They’re fighting,” I said jauntily, “and now it’s your problem.” “Stop fighting,” he intoned hypnotically, and they immediately did, but I took off with every confidence that they would start up again in 30 seconds.

The origin of most of their discord is TikTok or Instagram (unless it’s discord.com), and sure enough, a mighty row on cleanliness does rage among Insta-celebrities, who run the full gamut from Ashton “I wash my armpits and my crotch daily, and nothing else ever” Kutcher to Dwayne “I shower three times a day” Johnson. I’d say that’s pretty obviously a cipher for a conversation about masculinity. Kutcher’s the kind of man who is so manly that everything about him smells delicious (excepting his exceptions). Johnson’s the kind of man who produces so much manliness that only at its outer reaches can modern plumbing keep up with him. I would lean towards the Kutcher model. Some friends recently went to Berlin just to go regular clubbing, but by coincidence arrived for a leather-fetish weekend, where the bouncers at every bar smelt your pits to make sure you weren’t wearing deodorant, on the basis that it was sexier and more fetishy to smell of yourself. My first thought was that I’d like it if all bouncers did that. I shared this with the kids to distract them, and they hit pause on their argument only very briefly, to unite in the view that I am disgusting. Maybe they have a point.

The hair-washing debate is more complex than body washing; there is a school of thought, and has been since I was a kid, that the more you wash it, the greasier it gets, and true nirvana is reached when you stop washing it altogether, whereupon it starts to self-wash. This is what H thinks. The counterpoint is that self-washing hair is a myth; you could spend months looking like a grease-monkey to disprove it, or you could just wash your hair, which only takes 30 seconds anyway. This is what TJ thinks. I personally am of the view that any of these stances might be true, but not for teenagers, who can produce grease, particularly from their heads and faces, as you stand there watching them. They can also change age from toddler to 35-year-old and change personality from pure empath to raging sociopath, as if someone’s hit fast-forward. Don’t get me wrong, I wouldn’t change a thing, except to make one basic improvement to the operating model, that they’d stop bickering the whole damn time. “Nobody needs to be right,” I said, “just do what’s right for you. In Berlin they have a saying, ‘never comment on another man’s moustache, even if he’s dipping it in his soup’.” “Never,” they replied in unison, “say one more thing about Berlin.”