KEY POINTS:
Seth Rogen and Judd Apatow are hot. Not in the traditional sense - the former is slightly overweight with boofy hair and a penchant for weed; the latter has forged a film career by exploiting Rogen's weight, boofy hair and penchant for weed. But thanks to the runaway success of their new movie in which Rogen stars and Apatow writes and directs, they've emerged as a nerdy version of the Hollywood Brat Pack. Eat your heart out Ocean's 13 - Knocked Up is the funniest film of the year.
"We've gone mainstream. It's weird, " laughs Rogen.
He plays Ben, an immature slacker who impregnates entertainment reporter Alison (Katherine Heigl) during a one-night-stand, then tries to get to know her before the baby is born, the punchline being that she's completely out of his league.
A typical conversation:
"I'm pregnant."
"[expletive] off ... with a baby?"
Although rife with toilet humour, stoners and sex jokes - by the end you'll be completely desensitised to the word "vagina" - it's a sweet storyline about a couple who were never meant to be. And unlike the lewd laughs of Apatow's last juggernaut, The 40 Year Old Virgin, Knocked Up isn't just silly-funny. It's real-funny.
If you don't see yourself as either of the couple, you're bound to at least relate to one of their friends or family members, whether it's Alison's uptight sister who can't come to terms with ageing or Ben's doofus mates whose idea of an IT career is to start up a soft-porn website.
It's not a film for the easily offended but it's relatable to the point of discomfort.
A typical husband-wife scene:
He: "Shall we have sex tonight?"
She: "Ugghhh. I'm just really constipated. Do you really want to?"
"When I did 40 year-old Virgin I realised audiences are starving for movies which are a little more frank, that treat the audiences like adults," Apatow explains. "So I decided to be as honest as I can and go all the way."
He's not kidding about the honesty. Apatow's personal life inspires much of the script, as do anecdotes coaxed from the cast.
"We'd be sitting around talking and he'd be trying to fish stories out of your life," says Rogen. "He asked me, what is some really stupid stuff you and your friends do? I'd say, we put fish bowls on our head and smoke weed inside 'em. We see how long we can go without shaving for no reason at all. Watching it is weird for me - it might as well be documentary footage."
Apatow also asked family friend Paul Rudd, who plays Alison's sister's hen-pecked husband, the one thing he does that his wife can't stand, then wrote it into the film.
Then he hired Rogen's real-life best friends to play Ben's mates, not even bothering to change their names.
Alison's sister is played by Apatow's wife, Leslie Mann, and their kids play the kids.
"Usually kids are so stiff and awful in movies so it was fun to just throw my kids in the scene. It wasn't too hard.
"I would just buckle them into a highchair, put bacon in front of them and I knew as soon as they got full they would stop acting and want to go home."
He also encouraged the cast to improvise, leading to hilarious discussions about time machines, moving to India and a surreal sequence involving a Las Vegas hotel room, magic mushrooms and a row of chairs.
Apatow reckons his unconventional movie-making style is "more like a half-arsed Mike Lee" but it's a technique that has served him well for a decade. First came his cult TV show, Freaks and Geeks, in which Rogen played an uncool, pot-smoking high schooler.
Then came Undeclared, a commercial flop about a crew of dorky college kids, again one of them played by Rogen.
Apatow's first big score was with The 40 year old Virgin in 2005, starring Steve Carrell as the hapless virgin, and Rudd and Rogen as his crass workmates.
"We have a shorthand and we're very intimate with each other," says Apatow of his cast.
"I really know things about them that allow me to get them to do things on screen that other people might not get out of them."
Apatow wanted to make a film about babies next as he had a lot of material to draw on. He was also keen to put Rogen in a leading role for the first time.
"I always thought he was somebody I would root for. He's an underdog and he's both charming and vile at the same time."
Rogen, who had worked as a writer with Sacha Baron Cohen on The Ali G Show, helped to write Undeclared and co-produced Virgin, had plenty of ideas. Most involved ambitious science fiction plots. Knocked Up was born when Apatow told him, "You were funny in Virgin just sitting there.
"You don't need spaceships and aliens, you could just get a girl pregnant and that would be enough for an entire movie."
So Rogen not only gets the girl, he gets to procreate with the girl.
"I'm in on the joke," he says of playing the loser. "I'm a fan of movies and I know what the romantic, desirable lead looks like and I made it my goal to not be anything like that."
Heigl, one of the more popular stars from Grey's Anatomy, was an easy casting choice because she was the one person who was strong with Rogen in the auditions.
"A lot of the women would be sad when Seth would yell at them in these fight scenes," says Apatow.
"A lot of the movie is very confrontational. Katherine was the first person who gave as good as she got. He would yell and she'd scream right back."
There is also a lot of screaming in a particularly gruesome birthing scene. "I've always planned to adopt anyway but that definitely reinforced my want to," Heigl told USA Today. "I'm done with the whole idea of having my own children. It doesn't seem like any fun. I don't think it's necessary to go through all of that."
Now she's engaged to musician Josh Kelley, children are a likely prospect. But just because he's a musician doesn't mean he's anything like Ben and his mates, she says.
"Josh's friends are all musicians so they don't sit around getting stoned. They sit around making music. And that can be just as irritating sometimes. You're like, 'Can we have a conversation?' Instead of lyrics all the time?"
There was just as much noise going on in the audience during a preview screening for the film here. In the US, audiences laughed as hard as cash registers clanged, and the film went to number two at the box, pipped by Pirates of the Caribbean. Apatow suspects its success is partly because viewers need cheering up, what with all the bad news out there, and because "half the world is filled with goofy guys trying to get beautiful women who are out of their league".
He should know, titters Rogen, referring to his director as "no Brad Pitt" who still bagged a "gorgeous" wife.
And that's the essence of his success, says Apatow.
"All comedies are about underdogs. There's no great comedy about any incredibly confident, handsome man who can handle any situation. Whether it's WC Fields or Buster Keaton it's always idiots trying to figure things out that make funny movies, so I don't really think I'm doing anything different than what you see in any films by Harold Ramis [who has a cameo in Knocked Up as Ben's dad] or Bill Murray or Jerry Lewis or Steve Martin. It's all people in over their heads."
Lowdown
What: Knocked Up, the funniest film of the year, so far
Who: Actor Seth Rogen and writer/director Judd Apatow
When: From July 19 at Village, Hoyts, Rialto cinemas
