I've never clapped nor have I have been around people who have clapped at the end of a film except for when it was a screening and the creators, cast, and/or crew was there.
I've actually experienced that a few times (i.e., applause during a regular show time). It's always been at an exceptional movie. I think it may have also happened when I was at a sneak preview of RAIDERS OF THE LOST ARK in Tulsa (and I'm sure most of us agree that movie was exceptional).