EWAN McGregor does it in Trainspotting. Richard Gere does it in Breathless. Even Jack Nicholson does it in Something's Gotta Give. But when it comes to male nudity, William H Macy probably does it more often than anyone else.

"After I turned 50, every other film they wanted me to take my clothes off, " he says, affecting the look of deadpan dejection that has become his signature mannerism. "I've been in good shape my whole life. Why did they wait until I'm 50?"

He's at it again in Wild Hogs, showing off his butt in close-up as he goes skinny dipping with John Travolta, Martin Lawrence and Tim Allen. They're a group of mid-life crisis suburban dads who ride off on their Harleys for one last fling of uninhibited manhood. While the others insisted on a closed set and had to be given reassurances as to how much of their bodies would be shown, Macy dived straight in.

"Everyone thinks you're so brave and so bold and such a serious actor just because you drop your knickers, " he says. "It's not that big a deal, really. For some reason in this country people are so hung up about the human body, it's sick. I've never understood why you can take a young woman and disembowel her but you can't see her tits, because that's dirty."

All that bothered Macy about being marched down a prison corridor naked except for handcuffs in David Mamet's 2005 movie Edmund was that, after his scene, the prop guy lost the key.

"Low-budget is not for sissies, " he sighs. "I was buck naked in The Cooler, rolling around with Maria Bello. It's just hard to get embarrassed after that."

So what does his wife think?

"She's a fan, " he laughs. "But it's odd to be so intimate with another woman and then come home and not feel guilty."

His wife is hardly likely to be shocked. She's Felicity Huffman . . .

Lynette in Desperate Housewives.

She famously pulled out a penis to pee in Transamerica in her role as a pre-op transsexual. They married in 1996 and have two daughters but were together for 15 years before that. She was his student at the Atlantic Theatre Company which he set up with Mamet, and she acted with him in Speed the Plow and The Cryptogram.

"I've known her forever, " he says. "She's pretty insistent on us talking about everything, which I'm not inclined to do because talk leads to emotions and that's a slippery slope. I think it's God's little joke on us that men and women are so different and yet we need each other. Ours is pretty much a 50/50 relationship She likes me to be strong. One of the things she appreciates is that I'm fairly decisive about things. I think she leans on that."

Macy's screen persona couldn't be more different to how he is.

With his worried face and ringed eyes he's a natural for sad-sack loser roles. He won an Oscar nomination as an inept car dealer who hires hitmen to kidnap his wife for ransom in Fargo. In Magnolia he's an embittered one-time child quiz star, while in Boogie Nights he played a sleazy porn director, a role he prepared for by going to see a real porn movie being filmed. "Playing a role is a technique, it's not life. Something does happen you, especially if you're playing something dark like Edmund. You can get into a weird mood. But I can drop it. All this method thing about becoming the character, that's not acting. It's mental illness."

Just as Macy was Huffman's teacher, Mamet was Macy's when he switched from studying to be a veterinarian to do theatre at Goddard College in Vermont.

Later they got together in Chicago at St Nicholas Theatre, where his smartness with dialogue helped establish the character of Bobby in Mamet's breakthrough American Buffalo. Macy has been a regular in Mamet's movies, whether as the mafioso driver in Things Change, a marine in House of Games or an FBI agent in Wag The Dog.

"We had nudity on the stage years ago in Chicago, " he says.

"The first time you do it, it's a horror.

But then you realise you're strangely alone on stage, it's sort of private, and sooner or later you get this notion everyone in the room has something to hide except you. It feels oddly empowering. My initiation was in a play called Billy The Kid. Years after, every time I got lucky, sooner or later she'd say, you know I saw you in this playf" Mamet taught him that all an actor needs to know about a role should be in the text, which is why Macy prefers indie movies to Hollywood blockbusters . . .

although he did appear in Jurassic Park 3.

"The script is God, " he says.

"It's got to be solid. You don't have enough time to be figuring out what you're going to do. For some reason in the studio system they've a tendency to launch the ship without a map. The script is always in flux. It's idiotic. It's a stupid way to make a movie. It makes everybody unhappy and costs a lot of money. But that's the way they do it.

"So I was nervous about Wild Hogs. The first read-through was a little sketchy because the script wasn't fixed. I think I have to say it was disastrous. But then we had a training ride and got on our Harley's. We had such fun that we bonded like there was no tomorrow. And I loved my character, Dudley. His whole life is in crisis. But he's so brave and honest and straightforward and fearless." His eyes gleam. "And in the end I get the girl."

Macy worried initially about elements of homophobia in the script. "One of the themes is that these four guys really love each other, but Dudley is the only one who's brave enough to say it. I'm comfortable with all that. But there was a bunch of stuff we cut when I got up on my high horse saying if we have a doubt we have to cut it. If you couldn't say something about a Jew, a black man or a woman, you can't because someone is gay."

Felicity Huffman's success with Desperate Housewives means she's now the bigger breadwinner. "Because she's so well employed, I've ventured out into some areas I couldn't have been able to do, " he says. He's written and plans to produce The Deal, a romantic comedy with Meg Ryan about the trials and tribulations of a film producer. "In most romantic comedies you get two people born to be together and you keep them apart until page 110 and then everyone is happy.

But we sleep together on page 30.

It's grown-up and really subversive."

A far cry from Wild Hogs, which opened top of the US boxoffice charts three weeks ago and has grossed $140m. Huffman and Macy try not to be working at the same time so that they can have more time with their daughters.

"It doesn't always work out.

That's why as soon as Felicity's out of Housewives we want to go to New York and do something on Broadway. That's where we cut our teeth."

Buck naked again?

"Absolutely."

'Wild Hogs' opens next Friday