DISCLAIMER: CUSTOM ALTERNATE ENDINGS ARE MEANT FOR PEOPLE WHO HAVE SEEN THE MOVIE ALREADY. RUIN THE JOKE BY WATCHING THIS FIRST AT YOUR OWN RISK.
Also, it is strongly advised that you disable your favorite media player's function to show how much time is left (or go full-screen in such a way that the time left doesn't display) before watching, to keep yourself from being 'spoiled' and wrecking the joke.
A "custom alternate ending" is basically where I, just for fun, 'move up' the credits of a movie to a point that would change the ending, sometimes dramatically. It's all just for fun. Again, this is NOT a serious/normal release of a movie.
My first CAE is of Juno. Saying anything else might give it away, so I'll leave it at that. Enjoy!