The recent version of it is from Spider-Man 2, I believe. The snooty usher says to Peter, who's raced to get to a theatre show performed by Mary Jane, that "no one will be seated after the doors are closed; it helps maintain the illusion." Our poor hero, of course, has been off Doing Good Deeds and as a result his double-life has yet again foiled his chance to win MJ's affections.