So, I was only very recently made aware of this thing, but it is the greatest thing ever.
Basically what you are supposed to do is playing a movie you like a lot (you know, one that left a permanent impact on you or that you liked enough to warrant multiple re-watches, effectively to the point you left no details to be discovered) on your PC, and then go around looking for the subtitles of another, totally different movie in terms of the tone, genre... whatever works for you.
Ideally, you want to pick the subtitles to a movie that's at least equal on length to the one you are pasting them over (so you don't run out of them mid-way thru) but honestly, anything would do.
The true magic of this is that, depending on both of the source movies, the results can be very varied, and there's as many possible combinations as there's movies to combine. You seriously could turn a serious political drama into a laugh-out-loud comedy with just the right pick. Or you could turn a comedy into a musical, why not? The important thing is to try and see.
Just as a little demonstration, this is what happens when Harry Potter and the Prisoner of Azkabam meets the subtitles to the drama movie Detention. All image credits go to Akusoft.
Care someone to explain why is Hermione so in-character on this? xD
Incidentally, you can also try and feed the subtitles to Google first, for some amusing results:
Azkabam = Marriage.
TOO good xD
Anyway, have fun mixing stuff up! And feel free to share your results