The TV comic hasn’t quite got life worked out yet – and it’s very possible he never will. Romesh Ranganathan has legally been an adult for 24 years – he’s 42 now and has three sons – but it may take another 24 years for him to feel like a real grown up.

“I feel like I’m pretending to be a dad, pretending to be a husband, pretending to be a comic,” he says. “You fall into the trap of thinking everyone else has got their s*** together, and it’s only when you talk to people you realise nobody’s really got a clue.”

It might seem surprising, then, that his new book, As Good As It Gets, is as much life coaching manual as memoir, but Ranganathan reckons not having it nailed is good qualification for discussing what not having it nailed is like.

A 250-page arm on the shoulder, this book-of-all-trades rollicks through life’s most relatable mishaps, from the perils of parenthood to the atrophies of aging, concluding that a certain amount of failure is normal, unimportant, and rather funny.

Grumpy, self-deprecating, and drier than a desert, fans of Ranganathan’s stand-up will find the humour delightfully on-brand, but there’s also an honesty that can only come with genuine personal revelation.

The musings about married love life are both relatable and strangely touching (“there’s little chance we’ll wake the kids”), while at the other end of the scale there’s a fabulously vile anecdote revolving around diarrhoea. He spills the beans with heartfelt sincerity and gratifying vulgarity, sometimes both at once.

“Some of the things I wrote, I thought ‘Do I actually want people knowing that?’ But it’s the same as it is with stand-up. If you feel embarrassed to say something, that probably means it’s a good thing to talk about.”

It helps that, despite his protestations, Ranganathan surely has more clue than most. He has an impressive knack for observation – of his family, of humanity, and of himself. He points out society’s foibles by identifying them in his own behaviour – isn’t it interesting how ‘we’ do this, rather than ‘you’ – so manages to criticise without discomforting.

“It’s in a comedian to drill down on things,” he says, “and I’m always trying to find a take on something that hasn’t been explored much. We all do s****y things and behave selfishly, and I wanted to try and get to the bottom of why.”

“In one chapter I discuss how I cancel on people at the last minute, which is a s****y thing to do. But then I thought ‘why do I do that?’ I’m not trying to f*** them over, so there’s obviously something more to it.”

He’s a case study in the difference between identifying a problem and actually solving it, and one is reminded of that old adage, ‘do as I say not as I do’.

“I realise I’m deeply flawed,” he says, “but I accept I’m probably not going to correct it. I’ll try but the truth is you have to manage it. For example, I find my lack of organisation deeply frustrating and I’ve tried to tackle it, but sometimes you just need the self-awareness to accept it and factor it in.”

It’s all very down to earth, and also challenges a lot of the preconceptions you might have about being a stand-up comedian. He writes at length about his limited social energy and regular ‘foot in mouth’ moments, and finds it harder to negotiate the mums and dads at the school gate (his sons are aged 11, 9 and 6) than gig audiences of thousands.

“There’s a lot of stuff I say on stage I could never say in conversation,” he says, “and when you’re performing, people don’t judge what you say as much. It’s a weird dichotomy, but I feel less exposed saying things in a book or on TV than I would if having a personal chat with somebody.”

Much like one of his routines, the book rattles from topic to topic, with a few pages and jokes apiece shining light on most of today’s social issues. He comes out in favour of tattoos, his children, and good manners (“I have gone off at friends because of the way they have spoken to service staff”). He’s much less fond of racism, other people’s children, and social media.

The last notches particularly filthy reviews, especially since, as a professional comedian, it’s practically part of the uniform. “There are positives to it,” he says, sounding unconvinced, “but it’s just so brutal. It’s so faceless that people show the absolute worst sides of themselves.”

“It’s not healthy to have a direct stream of opinions on what people think about you – good or bad. When I’ve had shows or books out, the instinct is to look on social media and see what people think, but even if loads of people say they enjoyed it I’ll focus on the one person that didn’t. I very rarely log on and feel better afterwards.”

Mental health also earns its own chapter, and Ranganathan first attended counselling when he was 17. “Back then I was ashamed of it,” he says, “and I didn’t tell my mum because I thought she’d think I was nuts.”

Reflecting that there is “less stigma now”, he says: “I’d like to see schools helping children be more comfortable opening up. I know it’s the parents’ job too, and massive inroads have been made, but we’re still nowhere near where we should be.”

Parenthood sees Ranganathan at his most relatable, and he has little time for the one-size-fits-all parenting gurus that attempt to optimise child-rearing. There is no such thing as a parent that knows what they’re doing, he says, and those that think they do “haven’t got a full appreciation of what’s required”.

“Before we had our first kid, we thought we had it nailed,” he says, “but every day you have to make tens if not hundreds of choices about what to say to your kid in certain instances, and you make terrible decisions. I’ve been very honest with my children about it. I’ve said ‘look, this is my first time doing this’, and I apologise if I think I’ve called something wrong. I want my kids to know I’m a human being, and human beings make mistakes.”

“When your first child is born, you’re still the same person you were before and you’ve got to figure it out. You don’t have to be this all-seeing eye. As long as you care – everything comes from that starting point – you’re probably alright.”

Ever-present in his books, his routines, and (obviously) his life, his wife Leesa is his perfect partner-in-crime, and a valuable testing ground for – and subject of – his jokes. “I talk about her a fair bit,” he says, “but she’s so unbothered, it’s remarkable really.”

“It’s dangerous because she says ‘yeah you can say that’, and then when I joke about her, her friends are horrified. If there’s one thing I’d like to communicate to the general public it’s that I do get authorisation. She says it’s OK!”

As Good As It Gets by Romesh Ranganathan is published by Bantam Press, priced £20. Available now