“People expect me to be a gregarious party animal,” Seth Rogen chortles. “Which I am not at all. I am generally pretty reserved and I get uncomfortable in big social situations. I don’t really drink and if I do it’s not in a place you’ll run into me.”

So people do really expect him to be the party guy from Knocked Up and Bad Neighbours? He gets slapped on the back? He gets bought depth-charges?

“That is the biggest misconception about me,” he says. “They expect me to have one of those hats with beer cans on the side. Ha ha.”

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You’re letting us down.

“Yes. Drink beer from your hat, why don’t you.”

Rogen may not, in person, behave like a drunken lunatic, but much of the expected bluff good humour is in place. The deep, damp laugh that swallows so much of his onscreen dialogue also sucks up his everyday speech. But there is also a caution to his delivery.

Rogen has dialled everything down for his excellent turn as Steve "Woz" Wozniak, co-founder of Apple, in Danny Boyle's much-anticipated Steve Jobs. Unlike Michael Fassbender, who is no ringer for the titular protagonist, Rogen always seemed like ideal casting for his character. Portrayed as kinder and less driven, Wozniak, the coding wizard to Jobs's holistic guru, comes across as the conscience of the operation. Aaron Sorkin's script suggests that Jobs was rarely anything other than brutal.

“I was not trying an impersonation,” Seth says. “The film does reflect what he thought, but he would never engage in conflict the way he does in the film. But he said the emotions were all right and that was good to hear. He said that really was what it was like to be in a room with Steve Jobs and that is kind of terrifying.”

Did Rogen get a sense, when doing his research, of why people put up with Jobs’s rudeness? Was it simply that he delivered the goods?

“Yeah, you see it in Hollywood all the time,” he guffaws. “I’ve fallen victim to it myself. If somebody is brilliant at what they’re doing and believe you could be part of that then you tolerate it. All of a sudden you find yourself making excuses.”

The presence of the calm, generous Wozniak kicks back against any suspicion that genius and bad behaviour must be intertwined.

Genius

“Oh yeah. That’s a line in the movie: you don’t have to be an asshole to be a genius. There are a lot of geniuses that are assholes. But there are also a lot of geniuses who are super-f***ing-nice. Aaron Sorkin is unbelievably lovely to be around – and funny and friendly. I’ve been working with Kate Winslet in this film. She could get away with so much assholeish behaviour. That’s like having money you’re not spending.”

Seth Rogen knows of what he speaks. He is only 33, but he has been around the business since he began doing stand-up comedy at 13. Raised in Vancouver, the young Seth went on to write with his school chum Evan Goldberg. The breakthrough came when he secured a role in the influential series Freaks and Geeks. Created by Paul Feig and Judd Apatow, the show never had huge viewing figures, but it gave the world such talents as James Franco, Jason Segal and Rogen himself.

“It was very emotionally driven,” he ponders. “That’s the thing about Judd and Paul. I had been told that when doing stand-up comedy. Write from experience. Write what you feel. If you just write a bunch of jokes it won’t be as funny as it would if you really feel something for it.”

In 2007, Rogen starred as a layabout shaken by new responsibilities in Apatow's Knocked Up. That same year, Superbad, Rogen and Goldberg's comic treatment of their own teenage debaucheries, found Jonah Hill and Michael Cera playing variations on the writers' younger selves. Rogen had very much arrived. Over the past decade, he has been an unavoidable force in American comedy. He chortled in Pineapple Express and Bad Neighbours. He stretched himself in 50/50 and Steve Jobs.

He’s never really done anything else. What would have become of him if he hadn’t made it in “the business”?

“I have no idea. I’d probably be selling weed somewhere,” he says. “Look at what’s happening in Colorado. I’d probably be making better money than I am now.”

Well, I’m glad he brought it up. A member of National Organization for the Reform of Marijuana Laws, Rogen has made no secret of the fact that he wants an end to the prohibition of cannabis. Where are we with that? Has the liberalisation of laws in Colorado and elsewhere pushed the US unstoppably towards legalisation?

Smoking pot

“I don’t know. It’s interesting,” he says. “It’s moving forward in America. In Colorado it seems they’ve seen the light. But we’re shooting in Atlanta, Georgia, and there you can still go to jail very easily. It’s time they realised they have bigger fish to fry than a few people smoking pot.”

A little less than a year ago, Rogen found himself at the heart of global media hysteria when The Interview (remember that?), a comedy co-starring James Franco, so enraged the North Korean authorities that there were threats of a "merciless attack" on the US. Sony initially pulled the film when exhibitors panicked. Then it was allowed on limited release.

He can’t ever have felt that he’d be at the heart of an “international incident”.

“No, no. You never expect that’s going to happen,” he says drily. “But I think they were a worthy target. I don’t in any way think we were wrong in going after them. Some people said: ‘Why would you go after a bear?’ But they’re not a bear. Bears naturally go about their business. He’s an evil dictator who was endangering millions of people. Nobody could have seen that coming. It was unprecedented. But I wouldn’t do it differently.”

Rogen seemed impressively unperturbed by The Interview fiasco. Threats of bombings and boycotts loomed. The media wondered how a laddish roustabout concerning two journalists interviewing Kim Jong-un could become (no hyperbole) among the most controversial films of all time.

Meanwhile, Rogen chortled away. He lives quietly with his wife in LA. Is there anything about the pressures of fame that get him down?

“I can’t do ‘shrooms and wander around the city any more,” he laughs. (That’s “magic mushrooms” to you, old man.) “That was a big revelation. It makes doing stuff like that more difficult. Aside from that it’s not so bad. I don’t have to wait at a restaurant. I can’t do ‘shrooms in the city, but I get a good table really fast. Ha ha.”