The bad sub-titles that come to my mind instantly are Electric Boogaloo (for Breakin' 2), and The Armageddon, for Warlock 2. Electric Boogaloo speaks for itself, but The Armageddon? That title wins some kind of award for being apocalyptic and generic at the same time. Now, I enjoy putting the appellation "The Armageddon" after every title I can think of. Try this at home. March of the Penguins 2: The Armageddon. Brokeback Mountain 2: The Armageddon. Snakes on a Plane 2: The Armageddon. Star Trek: The Armageddon. See how easy that is? It fits for virtually every title you can imagine.
So what other bad sub-titles are out there? I always laughed at the one-two punch of Friday the 13th IV: The Final Chapter, and the immediate follow-up, Friday the 13th Part V: A New Beginning. I also think Star Trek: Nemesis is a rotten title because it is so damn vague. Don't Picard and crew face a "nemesis" in each and every movie (or Kirk and his crew, for that matter?) Each and every Star Trek movie could have been called "Nemesis." Maybe that's why it failed...the title means nothing. Why not just call it Star Trek: Bad Guys in Space?
I know some people don't like the Star Wars prequel titles, but for me they work. The Phantom Menace literally explains the point of the film: a villain in the shadows, a puppet master behind the scenes, a phantom unnoticed...but weaving his evil tapestry. Attack of the Clones might be a little lame, but I love Revenge of the Sith, because it reflects that original trilogy title, Revenge of the Jedi. Oops, I mean, Return of the Jedi.
Some other candidates for rotten sub-titles? Friday the 13th: Part VIII: Jason Takes Manhattan, Silent Night, Deadly Night 3: Better Watch Out!, Sleepaway Camp III: Teenage Wasteland, The Stepfather 2: Make Room for Daddy...