Man of the moment Chris Hemsworth shares his favourite dad joke

Interviewing Chris Hemsworth is like playing a match under lights at the MCG. The pitch is set under blazing studio lamps in an auditorium filled with the Thor star's entourage, and we have just 10 minutes after Richard Wilkins and before Sunrise. Much like the TV series Entourage, Hemsworth employs two of his best mates from primary school, Aaron Grist and Luke Zocchi, as his personal assistants. "They're a couple of mates of mine from school … we went to Heathmont College and Ringwood Primary School, played football together and now we travel the world together. It's a pretty cool thing."

Our chat takes place before a swish benefit at Sydney's Museum of Contemporary Art, where the Tag-Heuer ambassador is appearing to celebrate 55 years of the iconic Carrera. He looks as stylish as you would expect from an international action hero, casually dressed in a white T-shirt and loose black wool jacket, expensively-beaten black jeans, combat boots, and a silver ring hanging from his neck from a long chain. He's a bit sick with a cold, I'm told, but has braved wild weather to auction off a Carrera Calibre Heuer 02 (final price, $35,000) for the Australian Childhood Foundation. "I came with a suit but it was rainy and cold and I had this cashmere-esque jacket and I thought 'this feels super cosy and comfortable' – it's like chicken soup on rainy day."

While some people might collect shoes, or jackets, or watches, Hemsworth has one style weakness: boardies. "I like buying boardshorts. That's all I wear at home – I've got three pairs on underneath these jeans right now."

Despite growing up wearing Rip-Curl surf watches on his wrist, Hemsworth began to appreciate fine timepieces after Tag-Heuer gifted him a Carrera while shooting Rush in 2013. "Prior to that, it wasn't even in the conversation because they were out of my league. But after that I started buying friends [who] I worked with Tags as thank you gifts."

Hemsworth says he follows a reasonably strict diet to keep that famous rig in order. "I have an 80:20 rule, 80 per cent good, 20 per cent cheat," he explains. "There's so much good food and organic farming in Byron, it's just spectacular. I've travelled all around the world and that's the place we keep coming back to."

The 34-year-old now bases himself in the hinterland outside Byron Bay with Spanish wife Elsa Pataky, and their three kids, India Rose, 6, and twins Tristan and Sasha, 4. They live a fairly low key life, all things considered, with Hemsworth reading picture books to his kids every night. "I don't sleep as much as I'd like to – me and my wife talk about this a lot – it's a constant negotiation. I'm like, 'I just need 12 hours', and she's like, 'you're being ridiculous'. My wife can operate on six hours and be happy and pleasant, but me at six hours is just brutal."

He might have fame and fortune, but the actor says he's just a normal dad, and even offers up a classic dad joke to finish our brief meeting. "Why did the chicken cross the road?" he asks. "To get to the other side." Groan. "Why did the bubblegum cross the road?" he continues. "Because it was stuck to the chicken's foot."

And just like that, it's game over.