When Jason Segel ’97 stood completely nude in front of audiences across America, he got just the reaction he expected.

“I went, on Friday night, theater to theater with the director [Nicholas Stoller], and we always stayed for the full frontal scene because it’s a mixture of shock and confusion and laughter,” Segel said. “That’s right up my alley in terms of my sense of humor.”

Segel scripted the full-frontal nudity shots of himself in “Forgetting Sarah Marshall” that opened last Friday and took in $17.3 million this past weekend.

Segel has starred in “Knocked Up,” “Freaks and Geeks” and currently plays Marshall Eriksen in the CBS sitcom “How I Met Your Mother.”

In “Forgetting Sarah Marshall,” which Segel wrote, Peter Bretter, played by Segel, takes a Hawaiian vacation to deal with his recent break-up with his TV star girlfriend Sarah Marshall, played by Kristen Bell.

Segel has been writing ever since his days at Harvard-Westlake and is part of the Judd Apatow comedy clan responsible for such comedies as “Superbad,” “Knocked Up” and “The 40-year Old Virgin.”

“It’s a group of collaborators and we all read each other’s scripts and give each other notes and go to each other’s table reads and act in each other’s movies,” Segel told The Chronicle Sunday in a telephone interview. 

Segel attributes much of his success to Head of English Department Larry Weber, English teacher Mallory Tarses and Head of Performing Arts Ted Walch. Walch remembers directing Segel in the school production of “West Side Story” as Lieutenant Schrank and “You Can’t Take it With You” as Mr. Kirby. Walch remembers Segel as “a very hard-working, dedicated actor.”

“I did a summer workshop for actors and one of the sessions was led by casting director Deb Aquila, who asked me about Jason,” Walch said. “She recognized something special in him, and this led to a series of meetings that resulted in Jason getting a manager [Stacy Abrams], who is with him to this day.”

The first play Segel put on at Harvard-Westlake was Edward Albee’s “Zoo Story,” in which he played Jerry and worked with Walch privately.

“I was pushing myself really hard, but I kind of knew that we were onto something special,” Segel said. “When we put on that performance, it was easily one of the best moments of my life.”

Segel played on the 1996 state champion varsity basketball team with current professional basketball players Jarron ’97 and Jason ’97 Collins. He said that his favorite high school memory is not of playing basketball, but of ninth grade retreat when he paddled down the Colorado River.

“Me and Jarron Collins were in a canoe together, and I literally spent a week with him, sitting between his legs while we both paddled down the river,” Segel said.

He quit the basketball team his senior year despite the allure of winning a second state championship and instead focused on writing and acting.

“It was a tough decision, but being part of a team really influenced my acting,” Segel said. “It’s you and a bunch of other guys, and you kind of have to learn when it’s your turn to take the shot and when it’s your turn to set the other guy up. Comedically, it’s very similar to playing on a basketball team.”

Segel said that it was hard balancing writing “Forgetting Sarah Marshall” and shooting “How I Met Your Mother” at the same time.

“The secret is that on the television show any of the scenes you see me studying law on the computer, I’m really writing the movie,” Segel said.

The movie took a year and a half to write and film, Segel said, admitting that it was a pretty short time for the production of a Hollywood movie.

“The whole movie in general is kind of an amalgam of 10 years of terrible dating,” Segel said. “I’ve never been particularly good at it. My relationships usually end up with me getting dumped and some woman driving away from my house.”