Hollywood tends to do this with its own movies from time to time, hoping to draw in more viewers by dishonestly appealing to demographics other than the ones they originally intended, say, by making it look like a movie has a greater density of action scenes or body-function jokes than it really does...
...but what I'm talking about here is things put together purely for humorous purposes by students of the craft and put up online. The process is taken to hilarious extremes! Examples:
"The Shining" made to look like a heartwarming family comedy
"West Side Story" turned into a zombie movie
(see above link for both)
"Titanic" as a horror movie
"Brokeback Mountain" as an inspirational Christian film (called Moun† Brokeback)
The "Back to the Future" films as a gay love story (Brokeback to the Future)
"Jaws" as a love story (Must Love Jaws)
"The Ten Commandments" as a teen comedy (10 Things I Hate About Commandments)
I'm sure there are several more I'm not aware of yet. These clips are hilarious! But what I want to know is: what is this kind of thing called? Does a concise term exist that means "fake trailer edited together from a movie to make it look like a completely different genre"? If not, I want to invent one!