Why did men on a stag party get naked, why wouldn't women act that way?

THE skipper of the Blue Thunder, a chartered fishing boat moored at Swansea Bay, was hoping for a quiet afternoon last Saturday. Mark Thomas was taking a group of young men out for an afternoon's fishing on the grounds off the Welsh coast, where they were hoping to catch a few mackerel, bass and gurnard. But when Thomas briefly popped below deck to check on his paperwork, he couldn't believe his eyes when he returned: every one of his passengers had stripped naked.

The crew of an RAF rescue helicopter flying over the area were also amazed at what they were seeing. Circling in for a closer look, a quick thinking airman got out a camera and started filming. Which is how video footage of ten naked men on a fishing boat together, wielding, if you'll excuse the pun, more than one type of tackle, became an internet phenomenon.

It was, of course, a stag do. The stag, 25-year-old David Lloyd and his best man Nick Woore, also 25, both from Bristol, had originally planned a quiet afternoon's wine-tasting in the Welsh Valleys. But curiously, it hadn't worked out that way.

"It was pretty much a spur of the moment thing," said Woore of the moment the men decided to bare all to the elements. "The skipper went into his cabin and we thought we would surprise him when he came out. We were all naked when the helicopter came over us. What started off as a quiet fishing trip with a few beers turned into naked madness."

But why is that? Is it a weird repressed sexual thing, or is it even deeper than that?

Since humans could walk upright, best man wedding speeches have been littered with oblique references to outrageous stag do behaviour and the streets of stag favourites such as Edinburgh, Blackpool and Dublin spattered with vomit and bravado. In recent years, hens and stags have become big business. In an industry now worth millions, 43 per cent of Brits say they have travelled abroad to attend a hen or stag weekend, while the average price of a trip - excluding the food and the (presumably copious amounts of) drink - now stands at around 170 per person.

"There seems to be an increasing market of people looking for something to do," says Grant Thompson, manager of the enthusiastically named hen and stag events company Go Bananas, which was founded eight years ago and has offices in Blairgowrie, Newcastle and the south of England.

"People nowadays ask a lot more questions regarding the specifics of what they're going to be doing, whereas when we first started out if we got them in a hotel and got them to an activity, that would be the end of it.It really has turned into a phenomenon."

But if the stags and hens of today are increasingly picky about what they get up to on a weekend away, the tradition itself is as old as the hills. Historical documents suggest the stag do first reared its drunken head in Sparta in 5th century BC, where military comrades would feast and toast a soldier on the eve of his wedding (although not, presumably, send him a strippergram or throw him a foam party) as a way of saying goodbye to his bachelordom. It also became a popular pursuit in Victorian times, where gents would host a night to say goodbye to loud and loquacious friends who might be rather too embarrassing to invite round to the marital pad.

"It's a rite of passage," says consultant clinical psychologist Ronald Bracey, who specialises in male psychology. "They have these traditions in the armed forces, when you cross the equator, joining work, leaving work. They're deeply ingrained in society."

What doesn't seem to be so deeply ingrained however, in a nation usually known for its coyness on the beach, is nudity. Yet buy a few rounds in almost any pub up and down the country, and at least one story of male nudity - whether at a stag night, a rugby club or a military initiation - will inevitably sidle shyly out of the woodwork, usually accompanied by tales of copious beer drinking and general high jinks.

In the Highlands and the Orkney islands "blackening" is performed, which involves stripping the stag, covering him in treacle, feathers and possibly fishguts, then driving him round the local area on the back of a lorry. Rugby clubs too are notorious for performing initiation ceremonies involving nudity in conjunction with various degrading acts, while in November 2005, controversy arose after a video emerged showing Royal Marines fighting naked and intoxicated as part of a hazing ritual. One of those involved later explained it away by saying: "It's just Marine humour."

But why on earth do men feel the need - so aptly demonstrated by the Fishing Boat Ten - to strip off in each other's company?

"Competitive men together in that kind of context tend to try and outdo each other," says Bracey. "Unfortunately that sort of behaviour tends towards the negative. I call it bad boy poker. It's about upping the stakes. If one person does something, another does something even worse. It's totally competitive: who can do the most outrageous thing?"

That means the larger the group of men - and stags are getting larger, Thompson cites one stag party he hosted in Edinburgh last year involving 140 - the more likely it is that outrageous behaviour, including nudity, will take place.

"There is a diffusion of responsibility in a big group," he says. The collective of the group diminishes the outrageous aspects of certain behaviours.People do things within a group context that they wouldn't do as individuals because they're with other people, and that dilutes the moral and ethical aspects."

Behavioural psychologist Jo Hemmings says that a lot of the antics are simply about friendship. "It's male bonding. It's not sexual - it's what men do when they come off the rugby pitch. Men are quite happy stripping off together. It's very alpha male, the kind of thing you absolutely couldn't do in female company, which is why they probably do it. The alpha male is the one who can get the most drunk, who can be the most stupid - there's a lot of jostling for that pole position."

So it's not, presumably, the sort of behaviour you would indulge in when out for a drink with Arthur from accounts? "These things would only be done among really good friends," says Hemmings. "It's a way of saying we're all mates together. I don't think you'd get the nakedness if you were out with a few work colleagues or your fourth cousin twice removed."

Hens, meanwhile, a group of women single-handedly propping up the pink and silver Stetson industry in this country, are also capable of outrageous behaviour, although the nature of the event generally contrasts from that of a stag. "Women act very differently when there are no blokes around," says Hemmings. "But you'll rarely see a hen being humiliated in the way men are on a stag. Hen nights allow women to play out a role they wouldn't dare to if they weren't in that situation."

Although male strippers are now fairly common at hen nights, you're unlikely to see the women stripping off together. Zo Hughes Gough, publisher of Cutting Edge Guides, which issued the 2010 Hen Party Handbook, relates one tale that demonstrates how women are more likely to incorporate nudity into their hen night experience.

"We had a story about a group of hens who rented a lovely country house and for the daytime entertainment set up their easels in the light and airy conservatory, handed out 2B pencils, donned their artist's smocks and caps and revealed their subject matter - a toned and sculpted man, completely naked, for their inspiration," she says. "Obviously it caused a bit of a stir and plenty of giggles, but if you have an art tutor along too, you can actually learn something. Women don't always just go for straightforward titillation, they like to learn something too and express their creativity."

Hemmings agrees: "You're making an announcement on a hen night. There's no subtlety about it, you know when girls are out on a hen. It's informing the world around them of what hens do and allowing them to play a different role at the same time."

Some stag and hen traditions are less predictable.In the Shetland Isles, it's normal for not just the stag, but all of those involved in the event to dress up in drag, while one ancient Scottish tradition still practised today sees the hen being heralded through the streets by women banging pots and pans.

"It really is quite tribal," says Hemmings. "It's saying 'We're sending you off into another life, you're losing your freedom, this is your last night, we can all be boys or girls together'. Of course they wouldn't be doing that in normal life, it's very symbolic."

Bracey says such antics can be traced back to the beginning of time. "In primitive societies where belief systems are tied around representations of magic, rituals and rites of passage had huge importance in perfecting the caste system. It's really only a small extension of that which takes us into bad boy behaviour."

Which leads us back to our ten men on a boat, who appear to have absolutely no regrets about seeing their intimate moment of male bonding forever captured on camera.

"I have to admit it was pretty cold and windy," stag Lloyd confessed, once he had put his clothes back on. "But at least I can say I have had a stag do to remember."