Name: Underwear.

Age: The first loincloths date from about 7,000 years ago.

Appearance: Increasing.

You mean people are increasingly wearing underwear? No, they’re increasingly wearing it on the outside.

This is what happens when you let educational standards slip. They’re wearing it on the outside on purpose.

Why? Fashion. In recent shows Fendi had models striding the catwalk wearing skirts with matching bras.

What about their tops? Did they match as well? The bras were the tops.

I don’t know much about designer fashion, but this is a category mistake: the bra is a foundation garment. Nevertheless, the bra-as-top has become an established trend. It’s been creeping up on us for some time, with glimpses of bra beneath unbuttoned shirts.

And the shirt has finally been removed from the equation? Not always: at Erdem’s London fashion show, crystal bras were worn over the top of shirts.

I suppose if I had a bra made of jewels, I’d want to wear it on the outside. All kinds of bras are being reimagined as outerwear: tube bras, bandage bras, bralettes …

Bras for women who don’t need bras, you mean. Meanwhile, unitards are becoming popular for men.

They are not. They are: the single-piece “speedsuit” favoured by some elite athletes has started to work its way down to the amateur runner.

If wearing a mankini can help you win a race, it’s probably worth cramming yourself into one. The thing is, while speedsuits may enhance performance to some degree at a professional level, they’re not going to do much to improve your parkrun time.

So men are just wearing them because they like the way they feel? Or the way they look. “You have to have some level of audacity to wear one,” an amateur marathon runner told the Wall Street Journal. “And I think I have that audacity.”

The audacity to wear underwear in the street. He probably doesn’t see it that way.

If walking around in their smalls makes people feel modern, who am I to judge? Actually the underwear as outerwear idea has been with us for quite a while – corsetry was a popular fashion trope in the 1990s, as were slip dresses.

I suppose we have superheroes to thank for all this. While it’s true that Superman and others wore their pants on the outside, there is no evidence to suggest it ever caught on with the wider public.

Do say: “There is nothing new in fashion – let’s not forget that the ubiquitous T-shirt was once considered underwear.”

Don’t say: “It’s eight o’clock and the Uber is here! Why aren’t you dressed yet?”