When Robert Downey Jr's uptight businessman in Due Date assures an airport security guard "I've never done drugs in my life", at the screening I attended, there was a wave of chuckles. And I'm guessing there will be at every other screening around the globe.
This is akin to Russell Brand saying he's still a virgin. Or Ronan Keating stating that he has never made a bad record.
"Yeah, it was kind of hard, keeping a straight face for that one," smiles the 45-year-old former bad boy Downey. "There's some truth to it, of course, in that I am now a clean-living and upstanding member of society so, you know, I didn't feel my nose extending too far during that scene."
Having recently gone from being one of Hollywood's most notorious players (with the prison records to prove it) to one of Hollywood's key players in the past two years (with the box-office receipts to prove it), Robert Downey Jr is very aware of the incredible second chance at a glittering career that he's been given. Or is it his third? Fourth? Fifth?
"I've let many, many people down throughout the years," he nods, "none more so than myself really. I love what I do, and for me to have thrown that talent away again and again, to have abused other people's trust in that talent, and in me as a person, well, quite a bit of what I've done in the past is plainly unforgivable.
"To be in this position now, where I'm finally enjoying the career I was supposed to have 20, 25 years ago, that's both hilarious and humbling to me. And I appreciate it, totally.
"I'm one lucky, but hard-working, son of a bitch."
Hey, if only LA County Jail Prisoner No P50522 could see him now. Robert Downey Jr's attempts to make Keith Richards look like Daniel O'Donnell have been well-documented.
For several years in the mid to late ’90s barely a week seemed to go by without Downey Jr getting arrested for narcotics possession. He also did some serious jail time.
So when he claims that he has been drug-free since July 2003, you tend to believe him. Largely because it's taken the guy more than 20 years to be finally ready for his close-up. And bloodshot eyes might just tarnish his moment of long overdue glory.
That glory finally arrived back in May 2008, when Robert Downey Jr scored his first bona-fide worldwide smash with the Marvel comic book adaptation Iron Man.
It was a perfect piece of casting, Downey's decades of underground credibility finally finding a character that could take him overground. To the tune of $585m. Round two earlier this year did better, with a worldwide box-office take of $621m.
Just as Johnny Depp became an overnight sensation after a quarter of a century of cool with the box-office phenomenon Pirates Of The Caribbean, suddenly, all of Downey's years as an enfant terrible added to, rather than subtracted from, his immense talent as an actor. Downey was born to play the suave, sophisticated, sexy and sarcastic billionaire tycoon Tony Stark.
And now the man has a second franchise up and running, Downey today taking a quick break from shooting a sequel to last year's box-office-bashing rebirth of everyone's favourite Victorian sleuth, Sherlock Holmes. Suddenly, Robert Downey Jr has responsibilities. Expectations. And lots and lots of meetings.
"That's the one good thing about this upswing in work," he smiles. "I don't have enough free time to get into any trouble. I am so happy when I get a day off, and all I want to do is curl up in a ball and relax. The idea of going out and partying, well, it just doesn't cut it anymore."
Besides, the missus wouldn't allow it. Having met on the set of 2003's Gothika, Robert Downey Jr and Susan Levin married on August 27, 2005. Having worked as an executive VP for the notoriously loud and difficult Joel Silver (a man who reportedly held back 40pc of Downey's fee on Gothika until his work was complete), Levin was quick to bring some discipline and inject focus to Downey's career.
"The old saying is true -- behind every good man there's an incredible woman. I owe a huge amount -- if not all -- of my success to Susan. We make a great team, and all that luck I spoke about, that's Susan."
The couple have launched their own production company Team Downey, their first production being a remake of the Steve McQueen heist movie Yucatan.
"It's a different world for me out there now," says Downey. "Now, every day is a game day, and I love that. I love the challenge of it. I love getting to make the movies that I want to make. Do you know what it's like when you have an ego as big as mine, and you're third or fourth on the bill? That doesn't sit well with me. Unless, I've got a few big hits under my belt. Only then, can I play the humble supporting card."
A cough from the film PR reminds us that we haven't spoken much about his new movie, Due Date.
Directed by Todd Philips (Old School, The Hangover), Due Date sees Downey's uptight father-to-be and Zach Galifianakis' deluded would-be actor sharing a road trip from New York to Los Angeles, after they're both ejected from a flight.
The director himself describes it as "a buddy movie without the buddies". A more honest way to explain Due Date might be "a breezy, sleazy attempt to remake Planes, Trains And Automobiles, with the names, places and one-liners changed for artistic, and legal, reasons".
"Ah, you noticed," smiles Downey. "There are just so many stories to be told, and if you happen to have a cowboy in the central role, people don't automatically say, 'oh, they're remaking that old John Wayne movie'. There are similarities, but then, there are also similarities here with Midnight Run, with, with . . ."
"Yeah, I think you could say Rain Man -- although I'm not sure how Zach's going to feel about that one.
"He's [Dustin] Hoffman, right, not me?"
Due Date hits Irish cinemas today