Has Batman ever killed Superman?
There was a really messed up and depressing Elseworlds short where Kal-El's rocket hits Gotham, and kills Thomas and Martha Wayne. Bruce is horribly scarred (think, Two-Face, if someone took a blowtorch to his "clean" half), and Kal-El is adopted by Lex Luthor, who raises him as his son and teaches him how to be a bastard. One night, just before Clark Luthor is unleashed on the world, Batman crashes through a window, points a gun at Superman, and blows his brains out with a kryptonite bullet, before taking off his mask, and killing himself.
Yeah, some Elseworlds are messed up.