There isn't an easy way to sort movies by audience score using the RottenTomatoes interface. However, as mentioned by @Gareth,
audience_score is accessible through the Rotten Tomatoes API.
Obviously, in order to rank movies by
audience_score you need to obtain the scores for a given set of movies and sort them appropriately. In "Rotten Tomatoes Audience Scores" on rawdust, the author created a python script to do this for the
top_rentals list for the top 50 movies (this list is among the DVD Lists in the IO Docs and you could do the same using the list of top movies per the Box Office etc.).
The full python script is available here. (note: I'm not sure if it's "kosher" to cut and paste someone else's script in full here. If so, I'll edit appropriately).