Judd Apatow reveals his most hilarious, ridiculous behind-the-scenes moments

With movies like “Happy Gilmore,” “The 40-Year Old Virgin,” “Cable Guy,” “Anchorman: The Legend of Ron Burgundy” and “Bridesmaids,” Judd Apatow has been responsible for some of the funniest moments to hit the big screen in recent decades.

But, as the 57-year-old writer/director/producer reveals in his new memoir, “Comedy Nerd,” there’s been even more hilarity behind-the-scenes

The comedy bug bit Apatow early. The Long Island native was only 12 when, while visiting his grandparents, he chanced upon his then-idol Steve Martin outside his Beverly Hills home.

Apatow writes that he jumped out of the car to ask “The Jerk” star for an autograph and was crestfallen when Martin declined, explaining that he didn’t sign autographs in front of his home.

A furious Apatow wrote Martin a note that included a threat and dropped it in his mailbox.

“If you don’t send me an apology, I am going to send your address to ‘Homes of the Stars’ and you will have tour buses passing by 24 hours a day.”

Six months later, Apatow received a copy of Martin’s book “Cruel Shoes” that had the following inscription: Sorry, Judd — I didn’t realize you were The Judd Apatow! Your friend, Steve Martin.”

Apatow went to the University of Southern California (USC), then dropped out and tried to make it as a standup comic, when he met another struggling comic, Adam Sandler.

The two moved in together, with Sandler getting the bigger bedroom because he paid more.

“Nobody was ever funnier than Adam before he got famous,” Apatow writes, “when he had an enormous amount of comic energy and no outlet other than trying to make his friends laugh.”

For many years Apatow struggled to find his voice and took on rewrites, polishing scripts for friends. He admits that he found these situations stressful because “for some reason in my mind, I always thought, ‘if this movie fails, it is 100 percent my fault.’”

After helping Sandler on 1996’s “Happy Gilmore,” he began having panic attacks, which left him believing he was on the verge of a nervous breakdown.

The worst panic attack occurred during a meeting with Lorne Michaels about rewriting the Chris Farley/David Spade film “Black Sheep.”

“I hid that I was mentally shredding for the entire two-hour meeting,” he writes. “From the outside, I probably looked like I was listening intently, but on the inside I only had one thought the entire time: ‘If I have to get up and leave the table, I will just tell them I had some bad Pollo Loco.’”

Over the years, Apatow has worked with Will Ferrell multiple times to much success. In 2005’s “Kicking & Screaming,” Ferrell plays his kid’s soccer coach, and Robert Duvall is his mercurial father and competing soccer coach.

Apatow was brought in to produce the kid-heavy film after the original director was axed for daring to give Robert Duvall acting notes. He admits to being “terrified” of “The Godfather” star and avoiding interactions with him.

One day, Duvall cursed out one of the assistant directors so loudly that a parent of a child at the school near the shoot complained to SAG.

“I did not have the courage to be the one to handle the matter,” Apatow writes.

The Emmy winner directed the 2005 smash “The 40-Year-Old Virgin” and confesses that he struggled over how to portray Steve Carell’s long-awaited sex scene. Mentor Garry Shandling would constantly question him about the finale and kept pushing for the sex to be shown

“One day I was discussing this with Steve (Carell) and he said, ‘Maybe I could just sing a song’ … I immediately added something like ‘Let The Sunshine In’ from ‘Hair’,” Apatow recalls in the book. “This eventually led to an elaborate Bollywood type dance sequence, even though Steve and I had never seen a Bollywood movie before — but our choreographer had, I guess.”

Several years later he helmed another huge hit, “This is 40” and filmed the opening sequence on a brutally hot 117-degree day. “Everybody almost dropped from heatstroke,” he recalls.

Apatow writes that at one point, “an ice cream truck drove and the ice cream man, for reasons I still do not understand, was Joey Buttafuoco.”

He crossed paths with another notorious personality on 2007’s “Knocked Up.” The film starred Seth Rogen and Katherine Heigl, but adult movie star Stormy Daniels had a bit part in it.

Apatow remembers her coming to set and telling everyone she had just slept with Donald Trump.

“We didn’t think it was shocking of a disclosure,” Apatow notes. “Years later when he ran for President and it became a national scandal, all of us who were there instantly knew it was true.”

One of the strangest behind-the-scenes stories involves Joe Lo Truglio in 2012’s “Wanderlust” starring Paul Rudd and Jennifer Aniston. Production needed to determine if Lo Truglio would be flashing his real penis or a prosthetic one.

At first, Lo Truglio said he would be comfortable using his body, and then at some point, he decided to use a fake one. Special effects were hired to create a fake member, and, every day, a special effects artist would be required to glue a fake penis over a real one.

“Throughout the day, this special effects artist would have to constantly peer at it to make sure it looked ready for the camera and, when needed, adjust, add glue, push, pull up, and re-adhere the artificial penis,” Apatow remembers.

Another memorable moment involved Robert Plant. Apatow had an encounter with him years after the release of his 2007 music-bio spoof “Walk Hard” with John C. Reilly. The film had flopped at the box office, making less than $3 million and leaving Apatow so melancholy that his daughter dubbed it one of “the most traumatic experiences of her childhood.”

However, over the years, it became a cult hit and the Led Zeppelin lead singer told Apatow he was a big fan.

“That is the ultimate artbiter of success,” he explains. “If rock stars watch it on the bus over and over, then we have succeeded.”