I was watching "Demolition Man" recently and I thought of something that would greatly change the feel of much of the movie: She's his daughter but they don't know it! They probably go on to do everything that should not be done and wind up finding out only once they have a kid or something.
Then I thought "How many movies are there where a reinterpretation of key facts drastically alters how the movie plays out?" I was able to find a few from a quick google search. I only looked for a minute or two, but there have to be more out there.

Basically I wanted to see what other reimaginings of movies you guys have heard of or read or come up with or whatnot.
http://www.cracked.com/article_19266_5-movie-fan-theories-that-make-more-sense-than-movie.html
http://www.cracked.com/article/18367_6-insane-fan-theories-that-actually-make-great-movies-better/
http://egotvonline.com/2011/05/18/8-awesome-alternative-movie-interpretations/