There are friends of mine who are of the opinion that clapping at the end of a movie, as opposed to at the end of a play or a concert, is remarkably stupid. "Who are they clapping for?" they would ask. Others of like opinion would answer the question with "What a bunch of retards" and "Morons".
I, being of the clapping at the end type (but typically not when they're around), defend the applauders saying, "They're not clapping for the makers of the movie, they're clapping to show their appreciation for the movie; they're clapping for each other to show their enjoyment to each other." Well, at least that's what I think when I clap. I mean, I know none of the people responsible for the film are there. When I clap, it's because I enjoyed the movie, and if more people are clapping, that shows that the movie was well received by the audience and that I am affirmed in my opinion, all the while affirming the opinion of my fellow clappers.