There are a lot of comedians who consider themselves fearless or plain-speaking, but you would be hard-pushed to find anyone to match Doug Stanhope. Earlier this summer, the American comic was booked to appear on several bills at the Kilkenny comedy festival in Ireland; he managed to perform for just 10 minutes before having all his remaining slots cancelled. What on earth could he have said to cause such an uproar?

At the time, Ireland was in the grip of a paedophile panic, after a change in the country's statutory rape laws resulted in the release on a technicality of a convicted child abuser. And Stanhope duly added his fourpenn'orth to the national debate. Small wonder, he told his lairy, late-night crowd, that Irish men sleep with children, because - as the headline to the following day's Irish Daily Star put it - "Irish women are too ugly to rape! Comic booed after shocking festival jibe."

Putting aside for the moment what Stanhope said - and it wasn't quite what was printed in the Irish Daily Star - it's surprising that the Kilkenny organisers weren't prepared for him. Offensiveness is his stock in trade. His subjects - abortion, prostitution, school shootings (and that's when he's feeling upbeat) - run the gamut from morbid to horrific. But Stanhope isn't just another loudmouthed controversialist. His transgressive material is a means to an end: in my view, it softens up his audience for blisteringly honest perspectives on public and personal life.

The Kilkenny incident is a case in point: Stanhope says of the unlovely quip that got reported: "I didn't exactly say that, and I like my actual joke better. But what I did say couldn't fit in such a beautifully succinct soundbite." To be fair, there was a joke about how ugly Irish women are. But he also pointed out that, when it comes to rape, it isn't necessarily a greater offence if the victim is a 10-year-old or a 30-year-old: rape is bad, regardless.

Several Irish stand-ups in Kilkenny told me that it was "too soon" to joke about the paedophile brouhaha. But to Stanhope, that's absurd. "Everyone else in the country is talking about it. Why can't I? Anytime there's overkill on any subject, then yes, that's what I want to talk about. Especially when the hype is so retarded. But to have everyone in the audience go apeshit like that? It's not been since 9/11 in the States that I've seen people so touchy."

Does he care that he caused offence? "I write logically enough that I have no time for anyone who's offended. If you're offended, you're not listening. Or you're just a douche-bag. But in any case," he concludes, "you never know what the audience wants to hear. So I perform to myself, and on this occasion that's what I wanted to talk about."

He's been performing for 16 years, having switched from telesales to stand-up in 1990. His UK visits have been brief and infrequent, and if he's known at all over here, it's as the presenter of the credibility-busting cable TV atrocity The Man Show: "A woman-free zone," ran the spiel, "unless they're in bikinis or on a trampoline." (One exception to the rule was Stanhope's mum, who reviewed porn for the programme.) Stanhope doesn't even begin to excuse his involvement. "The show sucked," he says, "but I had to take the money.'" Now he has sworn off TV, and moved from LA to a backwater in Arizona.

His stand-up career betrays the same aversion to success and celebrity. He has largely eschewed the US comedy circuit, which is inimical to his brand of family-unfriendly comedy. "Anyone whose material is unique, comedy clubs are like, 'We don't know how that's going to play with our audience.' Well, that's because you trained your audience so that people who like something unique have stopped coming." His own shtick is certainly unique, and is the diametric opposite of what Stanhope describes as "the whole Seinfeld trickle-down of observational shit". These are not the words of a man bent on primetime fame.

So what motivates Doug Stanhope? "I am," says his popular MySpace website, "a comic, a drunk, and a lover of losers." His comedy veers between misanthropy and shafts of idealism; between tales that rejoice in his dissolute lifestyle, and those that strongly suggest Stanhope is deeply depressed. At one point, he tells me that "any TV show I do is never going to be as rewarding as what I could do live". The next moment, he denies that stand-up gives him any pleasure at all. "If I could make what I make on stage financially just by writing it, if I could put the material out there just once and never have to return to it, I would do that. I would not do stand-up."

I've seen Stanhope sabotage his own performances, out of boredom or anger. I fear for him in Edinburgh, where (for the first time) he's committed to performing for the full three weeks. How will he survive? "Poorly. That's how I will survive: poorly." The problem is, "I can't write enough to make up for how quickly I get bored with saying my own material. Especially at a festival - in my head every night I'm playing to the same people. And I feel like: they just heard this shit last night! I feel such a fraud."

So why does he keep doing it? Perhaps, like his forebear as America's pre-eminent comic seer, the late Bill Hicks, Stanhope is morally outraged by what he sees going on around him, and is on a mission to save the world. That used to be true, he says: "There was a stage when I was putting a lot of emphasis on how fucked up society is. But you get to a point where you go, why am I yelling about this? I'm just making myself miserable by realising my own impotence to change anything."

Now, he professes not to care: "My ultimate goal is just to amuse myself on any given night." But this is belied by his recent announcement that he is to run for president in 2008, on a noticeably idealistic platform: "This campaign will focus on individual freedom, self-government and making America fun again. And this campaign will wreak adrenaline-fuelled havoc across the land." He won't win - but he might open some eyes and carve up a few sacred cows. In the meantime, British comedy fans can vote with their feet for Stanhope in Edinburgh.

· Doug Stanhope is at the Comedy Room, Edinburgh (0131-226 0000), August 6-10, then at the George Square Theatre, Edinburgh (0131-662 8740), August 11-27.