Judd Apatow is best known today as the mastermind behind such blockbusting comedies as The 40-Year-Old Virgin (2004), Knocked Up (2007), Funny People (2009) and This is 40 (2012). But back in 1983, Apatow was a weedy high school student capitalising on a stint working at a Long Island radio station to meet his stand-up heroes.

Appearing on the doorsteps of such luminaries as Steve Allen, Jerry Seinfeld and Garry Shandling - giant tape recorder in hand - the young Apatow would ask his oft-bemused subjects about the frustrations of their early years, the origins of favourite routines and their own showbiz influences and inspirations.

Now a super-producer who knows everybody who’s anybody in American comedy, Apatow compiled his juvenile reporting for a book called Sick in the Head, adding fresh conversations with the likes of Adam Sandler, Ben Stiller, Jim Carrey, Lena Dunham, Jimmy Fallon, Jon Stewart, Key and Peele, Louis C.K., Sarah Silverman and Stephen Colbert.

Here, we cherry-pick some of the tome’s choicest revelations.

Freaks and Geeks was hugely autobiographical

The original comedy nerd, Apatow religiously recorded episodes of Saturday Night Live and The Merv Griffin Show as a teen, transcribing their monologues and sketches so as to better understand the creative process and learn the mechanics of humour. In turn, he passed these compulsions onto the characters in Freaks and Geeks (1999), the breakthrough comedy series he created with future Bridesmaids (2011) director Paul Feig starring a young James Franco, Seth Rogen and Jason Segel.

Apatow’s obsessions are threaded throughout the show. Sam’s bedroom walls are plastered with posters of Steve Martin and W.C. Fields. Neil goes trick-or-treating dressed as Groucho Marx (Judd once went as Harpo). Bill slumps in front of the TV after school eating grilled cheese sandwiches and watching Shandling reruns to forget his latest embarrassment on the basketball court.

But Apatow wasn’t the only member of the production team to bare his soul: Sam’s ill-advised decision to purchase a “Parisian night suit” from a disco clothing store and wear it to school was based on one of Feig’s greatest personal humiliations.

The cast of 'Freaks and Geeks' (NBC)

Amy Schumer says conditions are improving for women in comedy (sort of)

While Apatow expresses disappointment that the success of Bridesmaids hasn’t led to more female-led mainstream comedies – “There was almost zero follow-up in the culture… The studio system didn’t embrace them. They don’t know how to do it” - Schumer is more optimistic.

Conceding that she’s bored by the question, Schumer agrees that there are more opportunities becoming available but reflects, “All the TV I watched growing up featured funny women [too].”

However, her own experiences in Hollywood have been far from plane sailing: “There will be a script and you’ll be like, ‘This is funny, I think I’ll audition’. And you’ll know other women, who are hilarious, are auditioning, too. And then they’ll give it to, like, Jessica Biel.”

Chris Rock is a deeply wise man

As experienced a stand-up as you could wish to meet, Rock knows it all and is uncompromising and even unforgiving in dishing out tough love. Especially when it concerns self-pitying comics inclined to blame an audience when their jokes fall flat.

“Why do you give a fuck about the crowd? I mean, if you kill tonight, is the crowd going to get the credit? And so don’t give it to them if you bomb. It’s not them, it’s you.”

Chris Rock (Getty)

Jay Leno was once knocked out with a bottle of tomato sauce

The avuncular former host of The Tonight Show and famed auto nut began his stand-up career playing gigs at any venue that would take him, from restaurants to Indian reservations.

Taking to the stage in a strip club late one night, Leno was unceremoniously attacked by an unhappy costumer brandishing a Heinz ketchup bottle, splitting his head open and requiring eight stitches.

“Why did he do that? I don’t know. Why do people beat up grandmothers and rob their purses?”

Everyone’s a critic.

Jay Leno in happier times with Jimmy Fallon (Getty Images)

Racism in Hollywood is worse than you ever imagined

Representation continues to be a major controversy in American cinema, as the #OscarsSoWhite campaign has so amply demonstrated. The industry has come a long way since D.W. Griffith championed the Ku Klux Klan in Birth of a Nation (1916) but there’s still work to do, as illustrated by an anecdote told by Apatow himself in conversation with Girls creator Lena Dunham.

“I remember working on a black cop movie… There was a black character – a gigantic star – and in the movie, he had a romance with another black actress. And I noticed that they never kissed in the movie. I asked about this and the producer said to me: ‘Yeah. Internationally, people don’t like to see black people kiss.’ And you could tell the black star understood that as well.”

Dunham’s response is apt: “That is one of the most upsetting things I have ever heard.”

Roseanne’s unhappy childhood beggars belief

Perhaps surprisingly, Sick in the Head’s most moving interview is with the notoriously caustic sitcom star Roseanne Barr, who no longer performs due to chronic stage fright. Barr is open about her mental health struggles and frank about the difficulty of raising young children on the road.

However, her most remarkable confessions concern growing up Jewish in Salt Lake City, Utah, in the 1950s. Barr was raised in an apartment building with concentration camp survivors living next door and remembers being haunted by her parents’ obsession with watching the Adolf Eichmann trial on TV in 1961.

“It ruined my life… When they weren’t talking about Eichmann, they were talking about babies on meat hooks. They used to say it in front of me. I was so horrified at the world but I looked at the TV and it showed the pile of bodies, and I was like, ‘I don’t want to be on this planet’… The only time they talked to me was to tell me that the Nazis used to shoot little girls right through the head in front of their parents… They were all traumatised. Everyone was traumatised.”

She continues: “When I used to play Barbies with my Mormon neighbour friend, it was always, ‘Oh, we’re going to go on a date. Ken’s taking us out and we’re going with Ken on a date.’ And I was like, ‘We’re parachuting behind enemy lines to save the Jews.’ That’s how I played Barbies.”

Barr went on to have five children of her own and explains: “I was told when I was a girl that every Jewish woman has to have five children to replace three-fifths of our people that were killed. That’s how I was raised.”

Roseanne Barr (Getty Images ) (Getty Images)

Jeff Garlin is an evangelist for boxer-briefs

Best known for playing Larry David’s henpecked manager Jeff Greene on Curb Your Enthusiasm, Garlin is a delightful human being. The big man’s conversation with Apatow ranges from the day he lost his virginity (and, ultimately, clothes) at the beach to his all-consuming hatred for the work of Michael Bay: “Fuck him for wasting America’s time.”

But perhaps Garlin’s most heartfelt confession relates to his underwear preferences. “I’m a big boxer-brief guy. With boxer briefs, you get no ball fall-out… They hold everything in.”

Pushed to elaborate, Jeff explains: “There’s a certain confidence – I would have to drop my pants to show you. But I would not look like an idiot, whereas you, my friend, you wear tighty whities and we would be laughing at you.”

Jeff Garlin (Marion Curtis/Starpix/Rex/Shutterstock)