Alien is trying to watch a movie, but Predator is smoking a cigar and laughing loudly, disturbing everyone in the cinema. No wait, already been done.
Ummm...oh, I got one!
Alien has Predator's wife held hostage, so Predator goes to see them unarmed. Turns out he has a gun taped to his back, which he uses to shoot Alien. Alien goes out the window, but holds on to the wife's arm, almost pulling her out with him. Predator manages to slip her wristwatch off, loosening Alien's grip on her. Alien plummets to the ground, and the guy from The Breakfast Club says, "I hope that's not a hostage." Everything seems okay, until Alien #2 comes busting out the door, only to be shot by the dad from Family Matters.
The End.