Batman and Robin. It was really a tossup between that and Superman IV, but at least Superman IV did right by the character of Superman, even though the production value, writing, directing, and most of the performances were all garbage. Batman and Robin didn't even do that, and for all its production value it was an overblown, overproduced dud.
Keep in mind I haven't seen Catwoman or Jonah Hex. I suspect at least Catwoman would be a heavy contender for my least favorite. (Gotta love Ebert's review of it: "There are three things good about this movie: Halle Berry's face, Halle Berry's body,and Halle Berry's costume. Those are first rate. Everything else is unbelievably bad.")
Keep in mind I haven't seen Catwoman or Jonah Hex. I suspect at least Catwoman would be a heavy contender for my least favorite. (Gotta love Ebert's review of it: "There are three things good about this movie: Halle Berry's face, Halle Berry's body,and Halle Berry's costume. Those are first rate. Everything else is unbelievably bad.")