The Police Academy star stepped behind the camera to direct Williams in the 2009 dark comedy and admits he couldn't miss out on the chance to strip off and dive in as well.
He tells U.K. talk show host Alan Carr, "He's nude in the movie so for about half a day, we were just standing around with him naked... Sure (I joined him), it was hot! Not in a sexy way - temperature-wise. It was just like, how many chances do you get to dive off a diving board nude? So I just joined him. That's actually in the DVD bonus features."
And Goldthwait admits he was impressed after glimpsing a sight of Williams' nude body, adding: "I was like, I have no idea why you're so insecure. If I was hung like him, I wouldn't have pants on right now. I would be walking around all day (nude). I would just be like, 'Hey, how you doing? Check me out, b**ches.' (But) he did have to get rid of the hair for the scene."