The actor – who has been married to Pinkett Smith since 1997 – told the humorous anecdote during an appearance on the Graham Norton Show while promoting his new film King Richard, in which he portrays the father of tennis stars Serena and Venus Williams.
Smith said that he pulled the prank on his future wife when she met his family for the first time.
“I was raised in a very religious household,” he explained. “And my grandmother Gigi is all the way down with Jesus. Because she didn’t know who Jada was, I put on a movie of hers and worked out that by the time Jada arrived my grandmother would be watching the love scene.”
The 53-year-old continued: “When [Jada] walked in, my grandmother was in the middle of the scene and she looked up and said to Jada, ‘When I was growing up people didn’t have to take their clothes off to make a movie.’”
The I Am Legend star revealed that Pinkett Smith “took him aside later that night” and asked what he had been thinking.
“I said, ‘I promise you it’s funny, maybe not now, but one day this is going to provide us with years of joy,’” recalled the actor.
“We have been together for 27 years and she literally hasn’t chuckled once.”
Smith’s appearance on the talk show comes after the recent release of his memoir Will.
In the book, the actor makes a number of candid admissions, including that he developed a “psychosomatic reaction” to orgasms after a difficult break-up led him to have so much “rampant sex” it made him feel sick.
The actor’s appearance on The Graham Norton Show will air tonight (26 November) on BBC One at 10:35pm.