Look Ma - no pants! When did it become okay to flash your underwear in public?

The first Friday in May was International No Pants Day, a prank holiday in which all citizens in theory (and university students in practice) are encouraged to leave the house without trousers on. The point – and I admit it's a tenuous one – is to go about one's daily activities pantless, behaving as though this was the most normal thing in the world. It's funny, right?

That's what I used to think, too.

Last weekend, I was in Brighton, a lively seaside party town on England's south coast. The weather was glorious, the mood ebullient. The air tasted like sea salt and beef fat and a rare combination of sun, booze and Lady Gaga blasting from car stereos conspired to turn everyone – male or female – into a drag queen for the day. It was all about hair extensions and French manicured press-ons and platform sandals and glitter-dipped falsies on the boardwalk. And unnervingly, no one was wearing pants.

Maybe that's a slight exaggeration. I did see several pairs of shimmery black tights, diaper shorts and denim leggings (a.k.a. the lazy girl's skinny jeans), but that was about it. Gone, it seems, are the days when a well-placed miniskirt could cause a traffic accident. Today, a miniskirt will get you laughed out of a convent. The only option for getting a straight male's attention these days, it appears, is to leave the bottom off altogether, which means pairing a long T-shirt with high heels.

Personally, I was ecstatic when these long T-shirts started appearing in shops a few months back. It meant that I didn't have to worry about strangers on the subway seeing half my rear end every time I bent over to rummage in my handbag. Genius! I invested in a closet full. But it turns out I was misinterpreting the purpose of long T-shirts, which was to expose more, rather than less, of one's arse – only from ground up rather than the top down.

Imagine any outfit that Kylie Minogue has ever been photographed in and you get the picture.

It would be one thing if this trend were restricted to gay-friendly resort towns, but it isn't. While fashion magazines (and this section) will tell you it's all about floor-length hemlines and cardigans this season, a visit to any popular nightclub in the Western world will reveal scads of young women, regardless of age, colour, creed or thigh circumference, forgoing outer garments on their lower parts.

The question is, why? When did it become okay to show your underwear in public? What does it say about the post-feminist condition that so many of us refuse to wear the trousers that were once a mark of liberation?

As a rule, I find it hard to get excited one way or the other about what people choose to wear. I have friends in fashion, which means I'm used to people turning up for tea in top hats and fur capes. What I am bothered by is what they choose not to wear. In particular, I don't like having my face pushed in strangers' sweaty underpants. This was what happened as I climbed the crowded public stairwell up from the beach in Brighton. I won't be more graphic, except to say that it was an excellent reminder of why I didn't go into porn.

I grew up in a small town where the local diner had a sign reading, "No shirt, no shoes, no service." For hygienic reasons alone, I have always thought this was a sensible rule and, thankfully, one that most people who were not Camaro-driving, Mötley Crüe fans from Bewdley observed. But 20 years on, hick-town diners everywhere may be forced to add "no pants" to the list. This is unfortunate, not only because it ruins the alliterative value of the rule, but because it shows that, fashion-wise, we are actually moving backward as opposed to forward in time. As trends go, this one is surely a sign of the coming apocalypse.

I was at a loss, so I e-mailed the proprietors at Go Fug Yourself, a blog devoted to decrying red-carpet fashion crimes, to ask if they had any insights into the phenomenon. Within an hour, I had a response from "fugger" Jessica Morgan saying that she, too, had a hard time imagining why so many women are choosing to leave the house without trousers.

"I suspect this only happens with two sorts of people," she mused. "Those who follow fashion to perhaps a dangerously slavish extent and those who really want attention."

The good news, she added, is that in her estimation it's going to be a blip. "A year from now, we're going to be hearing from a lot of women who can't believe they went out in only their underwear. I truly don't think pantlessness works on anyone in a real-world situation – unless you're Rihanna, and the real-world situation is a concert you're in the midst of."

Take it from the fashion experts – pants are important. They cover our wobbly bits and separate us from the Muppets. Wear them early and wear them often and please ladies, if you see me coming, put on a pair for me.