Jack Black would never Expose his nipples ''just for fun.''

The actor rips off shirt in one of the peak moments of the video to his band, Tenacious D's track 'Tribute', and although it looks spontaneous, Jack insists it was part of The Script.

He told Q magazine: ''It was in the script. I would never expose my nips just for fun. That's serious business.''

Jack, 42, also claims he and Kyle Gass his musical partner in Tenacious D, like to go for ''Frisbee workouts'' while they are on tour, rather than hitting the gym.

He added: ''When we're on the road we go for Frisbee workouts. You know how dogs will run and catch a Frisbee with their teeth? Basically like that. Kyle will throw a Frisbee and I'll go chase it down and vice versa until we get a good lather going. But we don't go to the gymnasium together.''

Kyle added: ''Maybe we should?''

Jack has previously said he'd like to lose weight so he can appear in more nude scenes.

He said: ''When I saw my rear end in my nude scene in 'Margot at the Wedding', it actually had a double chin. I've joined a gym because the next time you see me naked I'll be trim.''