5. Cobra Commander (G.I. Joe: The Rise of Cobra)
G.I. Joe: The Rise of Cobra is by no means a good film, but I at least expected that they might have been able to get right one of the easiest villains to get right; even in the comics, the Cobra Commander was pure, silly pantomime. All they needed to do was suit him up in a cool outfit with a badass mask, and digitally alter the voice of which ever actor played him, and even if the film sucked (which it did), at least nobody would be able to complain that they totally ruined Cobra Commander. The result is a failure from the ground level upwards; casting Joseph Gordon-Levitt in the film is a bad idea from the outset (one of the few feet wrong the actor has put in his entire career), as his appearance - accentuated by scar make up - didn't really suit the comic vision of the character at all. To be fair, the recent sequel, G.I. Joe: Retaliation, did remedy some of these issues by giving Cobra Commander a shiny new suit and not revealing his face, but let's be honest, Retaliation was basically a secret reboot of the risible original anyway.