Three unknowns - Jonah Hill, Michael Cera and Christopher Mintz-Plasse - take the lead roles in new teen comedy Superbad. They tell Donald Clarkeabout sudden fame, friendship . . . and drawing penises

SUPERBAD, a fine new comedy from the people behind Knocked Up, concerns itself with the attempts of three high-school kids to secure booze for a potentially raucous party. Forced to rely on faked identity documents and the kindness of unstable strangers, the youngsters are driven to catastrophe by the constraints of the US liquor laws. It is, therefore, somewhat disconcerting to find each of the three stars I am to interview tucked behind a big, juicy pint of Guinness in a posh Dublin hotel. They all look very happy.

Yes, indeed. Jonah Hill, Michael Cera and Christopher Mintz-Plasse have landed. Within the space of a month, they have gone from being obscure actors or, in Chris's case, a totally unknown school student, to finding their unusual mugs plastered over buses, phone booths and hoardings. Today I find them deep in an explosively vulgar media hubbub. Dolly birds in Superbad T-shirts hang off their arms while tabloid photographers shout instructions. What have they let themselves in for?

"I walked down the street where I live in LA and went to get a haircut," Hill says. "I had walked the same way the previous day without comment, but now, after the posters went up, 10 people stopped to have their picture taken with me and people were saying these strange things to me."

It is impossible to wholly ignore the points of comparison between the actors and their Superbad personae. Christopher Mintz-Plasse, plucked from obscurity at an open audition, plays the nerd and, clearly in no great hurry to shake off that image, has turned up to the interview wearing a leprechaun hat with attached red beard. Michael Cera, known for his appearances on the cult TV show Arrested Development, portrays the sensitive thinker and, sure enough, quickly declares his intention to write his own material soon.

Jonah Hill? Well, Jonah, the corpulent, sexually-frustrated loudmouth in the picture, is 23 years old and, strangely, looks it. How on earth did he set about turning himself into such a convincing school-kid?

"I think that was the biggest acting challenge I've yet had," he says. "I moved back in with my parents and stayed in the room I grew up in. I tried to channel those early years. Luckily I haven't matured a copious amount."

"Yeah, but I bet you wouldn't have said 'copious' back then," Cera interjects.

"That's right. I would have said 'shitloads'. Actually, those are the things you have to think about: I must not say 'copious'. I must say 'shitloads'."

The gang have just finished a tour of Britain and are gearing up for an invasion of mainland Europe, but they still seem to be getting on quite well. I wonder if, being the oldest, Hill has taken on the duties of de facto leader.

"No. I am in the middle of the poster, so I suppose people assume that," he says. "But we are all in charge of ourselves I guess. Actually, yeah, we do get on surprisingly well. We have not had a serious blow-up of any type yet."

"Maybe in Rome," Cera says. "Then we can have a fight and burn a few bridges."

The leprechaun remains silent.

It's nice to hear that they get on. Mind you, many observers have noted that, in the film, the characters played by Cera and Hill get on very, very well indeed. Search hard and you can find homoerotic subtexts in everything from Butch Cassidy and the Sundance Kid to Pinocchio, but Superbad must be one of the gayest straight films ever made.

"Oh, I wish we could put that on the poster," Cera says.

At the mention of homosexuality, Hill, who starred alongside Seth Rogen, co-writer of Superbad, in Knocked Up, begins a long, detailed answer to an entirely different question. He points out that the homophobic jokes in both films are meant to be seen as the ravings of idiots and that the writers are not trying to set an example for others.

Well, yes, fair enough. But what about the extraordinary affection between Hill's and Cera's characters in Superbad? It's like Brideshead Revisited with tequila shots.

"It's not homosexual," Hill says. "It's about two guys who can love one another platonically. Hey, I love these guys here. That doesn't mean I want to put my penis in any of them."

"What do you mean, you don't want to put your penis in me?" Mintz-Plasse says in mock outrage.

"Yeah. Now maybe we are having our first fight," Cera adds.

Hang on a minute. In one early scene, Hill's character reveals that for many years he had an obsession with drawing penises. Elsewhere he admits that he really enjoys pornography only when it involves the male organ. You don't have to be Sigmund Freud to infer certain homoerotic leanings in the character.

"Yeah, maybe," Hill says.

Astonishingly this reading really does not seem to have occurred to him. Surely he must have asked writer Seth Rogen - the fact that the character shares the writer's first name must be significant - about the reasons for the young man's phallic leanings.

"I think it is more about finding penises funny than the homosexual side of it," Hill ventures. "He is so immature that he finds drawing penises funny. I didn't really take it as being a version of Seth Rogen anyway. Who needs two Seths on set? I just saw it as these two friends wanting to stay together after school. I didn't see that as gay."

Oh well. Perhaps I am reading too much into too little. At any rate, the Superbad boys seem unperturbed to discover they may be in the year's biggest gay comedy. They are too busy drinking pints, frolicking with photographers and dressing as dwarfish mythological cobblers.

"Yeah, I do tend to get freaked out when things are this awesome," Hill says.

"This is like the most exciting thing in my career and I just get freaked out thinking: can it really stay this good for much longer?"