Here is Peter Sellers in the hilarious outtakes sequence at the end of Being There, the 1979 Hal Ashby film that was the second-to-last film Sellers made. When I was a kid I thought this was the funniest thing ever. Blooper reels were rare in major Hollywood films back then, so I’d never seen anything like it. I remember feeling amazed that I got to see secret scenes that weren’t in the movie. Quaint, I know.
According to the Wikipedia page for the film, Sellers supposedly didn’t want the outtakes to be included in the movie, “since, by all accounts, it was his attempt to show his skills as an actual actor as opposed to just a comedian. The inclusion of the blooper reel is sometimes blamed for Sellers’ failure to win that year’s Academy Award for Best Actor.” I find that last sentence hard to believe, but who knows.