8. Jealousy
In World's Finest #85, DC's two most enduring superheroes were forced to contend with the single most powerful force on the planet. Not Fear, or Darkseid, or even a super powered Emperor Joker; instead, they battled the twin evils of love (or at least lust), and jealousy. When the delectable Princess Varina of Balkania visits, both heroes forgot their pre-existing relationships and attempted to woo her like a pair of giddy teenagers turned on by a shapely pair of breasts or a comically tiny skirt. Naturally, this inspires the untold wrath of Vicki Vale and Lois Lane, who are spurred into action to take back their men. There's more to the story, of course, as it turns out Varina is in love with a soldier (deemed unworthy of her hand in marriage) and Superman and Batman are simply attempting to stop her from trying to marry him, thus extinguishing their lovers' desires to kill the unfortunate, besotted Varina. So, at one stage, Superman and Batman literally fought love and jealousy. Talk about wasted comic book space.
Why It'd Suck Do you really need this spelled out for you? Friction between Batman and Superman is key to the success of the project - the same way Iron Man and Captain America grind against each other in The Avengers, and some of that should come from Batman's envy of Superman's powers, as well as from the inevitable clash of egos, but the idea of the pair clashing over a chick is the stupid extreme to that. To be honest, this point is representative of something else - while it's important to have the friction between the characters, it would be hugely reductive if the characters are played off each other so much that we end up with 120 minutes of forced banter, with deep sexual undertones, as Batman and Superman glower at each other furtively, flexing their muscles and making a play for who the better superhero is. The action should play upon that slightly, but too much focus, and we'll end up with Top Gun with capes.