The Muppets screenwriter and star played lead character Peter Bretter in the Judd Apatow-produced hit 2008 comedy, which he also wrote.
Asked if his mother had forgiven his full-frontal scene, he told Metro: "My mother has forgiven me because that scene really, truly wasn't gratuitous.
"It pushed the boundaries but was very much in the context of the event, which was the most painful break-up ever. I think that's what made it funny.
"Every time it felt too serious, we'd cut to a wide shot and see me naked. Instantly, people either laughed or threw up."
Segel added: "I'm not a conventional leading man. Hollywood wasn't knocking down my door to play Captain America. But people like to root for the underdog.
"I'm just not that compelled by people who get women easily and everything comes to them. We hate those people, right? That's not what my life has ever been like. I like having to fight for things."
Watch the trailer for Forgetting Sarah Marshall below: