13. Alien vs. Predator
A prime example of two classic movies being shoved into the same oven with less than appetizing results; we can't remember anyone who actually bought this as a concept. Arguably the two best extra-terrestrial badasses battle it out under the Antarctic ice, but this belligerent union is (like the hybrid creature the two life forms inevitably produce) definitely less than the sum of its parts. Despite the genuinely good video game that has resulted from the Alien vs. Predator crossover franchise, it's safe to say that this particular amalgamation has been relegated to the hall of crappy taste forever.