I guarantee you it happened, and several of my friends confirmed similar experiences. A quick google search also reveals that I'm not alone (e.g. http://thesmatter.wordpress.com/2011/07/30/review-of-the-audience-of-midnight-in-paris/ ). It shouldn't be surprising that the audience reacted that way, because the film was intentionally directed as an exercise in SWPL ingratiation -- the historical characters are winking cameos with no discernible purpose except to prompt viewers to pat themselves on the back for their literacy, while the conflict between Wilson and his fiancee is set up in order to vilify bourgeois materialism, a favorite target of trendy liberals (who ironically are bourgeois materialists themselves). What I experienced is every bit as believable as blacks chimping out during a Wayans bros film.