William Shatner loves to use 'juicy' F-word

William Shatner enjoys using NSFW language and isn’t afraid to admit it.

After delivering a keynote speech at the South by Southwest festival, Shatner spoke with producer Tim League about where his fondness for a certain four-letter word originated.

When asked what he thought about disruptive electronic gadgets, the 91-year-old "Star Trek" star said, "Shut the f--- up. I understand f--- is ugly to you. But it's a juicy word."

He even turned to the sign language interpreter and joked, "Shut the f--- up," before asking for him to teach the F-word in sign language, which made the crowd laugh.

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Shatner was also at the festival to support his new biopic documentary, "You Can Call Me Bill," following his six-decade career as an Emmy-winning actor, author, singer and activist.

During the panel, Shatner was reflective on his acting career, sharing stories about his more memorable moments in show business.

He explained he got into acting while attending a summer camp and had support from his father, Joseph.

"There was boxing, but then we'd put on a play. And I made the audience cry, and I thought, 'Look at that, I made them cry,'" he recalled. "My father, who had come by, said, 'My boy Bill, you made the audience cry.' Now my father is giving me love. I liked this. I think I will do it again."

Before landing his breakthrough role on "Star Trek," Shatner worked in theater and even worked as an understudy for fellow Oscar winner and fellow Canadian Christopher Plummer.

"He was playing Henry V, so Chris Plummer, who had become an acquaintance, was playing King Henry. So, the director said, 'You have to understudy the role.' It was repertory theater, so we rehearsed a play before we opened for a month or so," said Shatner.

"In the first week of opening the Shakespeare play, Chris Plummer got ill, and they came to me and said, 'Can you go on?' I said yes. I didn't know the names of the actors. I did not know where to walk. But what I did know was the actor's muse had been on my shoulder, and the actor's muse said to me, 'Learn the words.'"

Of course, it was the sci-fi series "Star Trek" that made Shatner a household name in 1966 when the series debuted.

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The show only lasted three seasons but has had an indelible mark on pop culture. When asked if the show was a "failure," Shatner denied it.

"Failure? Not quite a failure. ... It was a good show. It had some wonderful stories to it. Great ideas given to us by many great science-fiction writers like Isaac Asimov. Some of the ideas were marvelous," he said.

He did admit he struggled a little after the cancellation, returning to theater for a time.

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Perhaps the biggest surprise is that he performed stand-up as Captain Kirk.

"Oh Lordy lord ... Well, I thought it was very funny I was asked to do stand-up comedy," Shatner revealed. "There is nothing more pure and innovative, and it requires genius. I thought it would be really funny to be Captain Kirk who wants to be a stand-up comic, but he doesn't know how to do it."

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However, the reception wasn’t quite what he hoped.

"And there was silence," he recalled. "Oh s---, this isn't going well. It was probably the worst thing that ever happened to me. When I came off the stage, I slunk off, and the manager looked at me and that was it."