Sounds like a terrible idea. Everybody knows that smart, well-behaved players work together against the endless NPC hoards of the Dungeon Master. That's just common sense.
Apropos of nothing tonight, though, I started reminiscencing about a fun little scenario I played back in high school.
My character was hired to sail to the remote Isle of Dread. There, to capture and return with a prized man-sized dinosaur. Hey, Jurassic Park was new, so dinosaurs were sort of a thing.
The twist was the second player in our group of three that night was playing the dinosaur! All things considered, it went really well. Very tense, with lots of good-natured rivalry and tense hit-and-run action between the rivals (since the "monster" was also one player's sole game avatar, caution was key). Play took place in adjacent rooms, occasionally, to facilitate the sharing of secret information with the DM, but that did give one time to plot!
In the end, common sense got screwed and a great time was the result.