Jon Ronson is rummaging through a bag at home in upstate New York but stops, mid-search, to recollect the effect of learning to identify psychopaths.

“I got drunk,” he says, his hand still in the knapsack. “I got drunk with the power of my psychopath-spotting skills.”

He stares through his familiar, trademark round glasses towards the window. “I started diagnosing anybody who’s ever given me a bad review as a psychopath,” he says. “Like Sherlock Holmes, identifying psychopaths through the nuances of their language and behaviour. But then I learnt a lesson.”

Ronson drops the bag and drinks from a bottle of beer. “I realised my psychopath-spotting skills had turned me psychopathic,” he says, “because, it’s a little bit psychopathic to define people by the extreme, outermost aspects of their personality, the items that would get you labelled psychopathic on the checklist.

“You forget people are a complicated mix of positive and negative traits. That made me much more empathetic about people’s flaws and failings.”

Ronson, the award-winning Welsh author, journalist and screenwriter is known for his immersive, humorous and scalpel-sharp writing across various topics. He started exploring the concept of psychopathy in 2009.

It began at a friend’s house as he leafed through a copy of the Diagnostic and Statistical Manual of Mental Disorders, the American Psychiatric Association’s professional reference book on mental health and brain-related conditions.

In minutes, using the symptom checklists, Ronson had self-diagnosed 12 disorders including generalised anxiety disorder, nightmare disorder, parent-child relational problems and malingering.

Was he right? Entirely unqualified as a medical professional, it was debatable. But, he pondered, was the psychiatry profession possibly labelling some normal behaviours as proof of mental disorders?

Ronson’s intrigue led to The Psychopath Test: A Journey Through the Madness Industry, an instant hit that topped the New York Times and Sunday Times’ bestseller lists for months.

A rollercoaster of humorous and disturbing proportions, it catalogued Ronson’s meeting with psychologists, psychiatrists and psychopaths, some in positions of corporate and governmental power, some in psychiatric facilities such as Broadmoor Hospital.

Ronson loved every minute of it. “The narrative of The Psychopath Test is I am told by a Harvard psychologist that you’re four times more likely to have a psychopath at the top of the tree than at the bottom,” he says. “So, of all the mental disorders, the one that capitalism rewards is psychotic psychopathy. Which is kind of ironic.

“It’s the worst of all the mental disorders, the cruellest one, with no empathy or remorse, the one with impulsive behaviour, irresponsibility and glib charm, that’s the one that gets rewarded and propelled to the top and makes the world go around.

“It was just such an extraordinary thought. Now, I would say, it’s more known, the idea that we’re more likely to have a psychopath at the top of the tree – but 15 years later, it seems like a good time to revisit it.”

In November, Ronson is heading to Australia for Jon Ronson’s Psychopath Night, in which he looks at the book’s impact, shares fresh anecdotes and introduces mystery guests.

“Society is much more psychopathic now,” he says. “Social media has made us more psychopathic, along with the overuse of public shaming as a public weapon. There’s a lot to talk about.”

The Psychopath Test was not the first introduction to Ronson’s obsessive and self-analysing dives into society’s margins and mainstream.

His 2001 book Them: Adventures with Extremists, in which he interviewed Ku Klux Klan leader Thomas Robb and radical Islamic activist Omar Bakri Muhammad, among others, was followed by The Men Who Stare at Goats, about US Army paranormal pursuits, adapted into a film starring George Clooney.

Other books, including So You’ve Been Publicly Shamed, exploring social media fury’s effect on individuals, screenplays for films Frank and Okja, numerous radio programs, and podcasts including The Butterfly Effect, The Last Days of August and Things Fell Apart, prove one part of Ronson’s personality.

“I am happiest working,” he says. “I sometimes go hiking in the afternoons here but I haven’t taken a day off in decades. What else would I do? Just sit there, staring?”

He was recently forced to do nothing for two days while recovering in hospital from a blood clot. “I listened to Barbra Streisand’s 48-hour-long autobiography, of which a good four or five hours is her reading out excellent reviews she’s had over the decades. ‘Miss Streisand’s radiance is overwhelming.’ That was hard work.”

Ronson’s curiosity about the world, his enthusiasm to investigate and write stories of his adventures, is only matched by his friendliness and unassuming nature. He recalls his last trip to Australia in 2011 where he unexpectedly shared a hotel lift with Taylor Swift. “Nothing happened,” he says. “I just stood in the elevator and she got out. “That’s not a great story.”

It brings another story about fame and his friend, UK radio broadcaster Zoe Ball. “In the ’90s she was pretty much as famous as anyone in Britain,” he says. “Paparazzi in the bushes, Kate Moss level of fame. I always remember her saying to me: ‘You’ve got the perfect level of fame.’ Just enough to massage your ego but not enough that it interferes in any negative way in your life.”

Ronson can interview extremists, psychopaths, porn stars and people internet-shamed into obscurity but he can still savour a beloved two-hour train trip between the Manhattan apartment and Catskills house he shares with wife, Elaine Patterson. “It’s tourist-worthy,” he says. “The mountains, the sunsets bouncing off the river, it’s never a hardship travelling back and forth.”

It’s nothing like a recent train trip in London, the city where he established his writing career after leaving his hometown of Cardiff, aged 18. “It was horrendous,” he says. “There was flooding so about five trains’ worth of people got on our carriage. There were all these old ladies, all exhausted-looking and nobody would stand up for them. I gave an old lady my seat and, for the rest of the day, I felt so good about myself.”

He is reminded of this because he is reading Infectious Generosity by Chris Anderson, the head of TED. “One chapter is about how you don’t realise what an act of generosity will do to you until after you’ve done it,” Ronson says. “If I hadn’t given my seat up to that lady, I would have spent the whole rest of the day thinking I’d done something wrong.”

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“Psychopaths don’t have any of these feelings,” he adds. “No distress, no remorse, no guilt. That always makes me think psychopathy must be the most pleasant of all the mental disorders.”

He swigs a drink and smiles.

“I was slightly annoyed that nobody recognised me and tweeted about what a selfless act of generosity I’d performed,” he says. “But then I thought, my happiness about doing a generous thing isn’t reliant on external praise on Twitter. You’re the only person I’ve told that to.”

I promise to spread the word. “Thank you,” he says.

And he waves goodbye, unlike any sort of psychopath.

Jon Ronson’s Psychopath Night, Hamer Hall, November 20; Sydney Town Hall, November 21; QPAC Concert Hall, November 24; Canberra Theatre, November 25.