Colin Farrell feared that his mother would accidentally watch his sex tape if it was released publically.
In 2005, the 37-year-old star was offered $5m for the rights to the tape he made with Playboy playmate Nicole Narain, but he sued his former fling to stop the sale and distribution of the footage, though it later surfaced online.
He said that he took action because he found making the video "horrifying" and was worried his mother might accidentally stumble across the footage.
He told the new edition of America's Elle magazine: "It certainly wasn't a validation of my prowess. The whole thing was horrifying. You know, press record. Taboo. Isn't this interesting?
"I was deposed for four hours explaining why I didn't want it to be released. God forbid it's an on-demand movie in a hotel room and my mother says: 'Oh, I haven't seen this work of my son's, and hits 'purchase'!"
Farrell also revealed that he was "terrified" when he first had sex sober.
The Irish actor had a very "gentle" experience with a woman after giving up drugs and alcohol eight years ago, but found it nerve-wracking because it was so new to him.
He said: "I made love to a woman about two and half years after I got clean, and it was one of the most terrifying moments of my life. It was in the afternoon. The windows and the curtains were open.
"It was lovely... she was very gentle. But it was terrifying.
"Because I was just used to drunkenness and dark rooms and clubs and toilets and wherever.
"I worried I wouldn't be able to talk, full stop. I hadn't uttered a word sober in about 15 years."