I think that there are actually two types of books that would fall squarely in this category; modern bestsellers and classic novels. A lot of the classic novels are well-known, but how many people have actually read Wuthering Heights or Moby Dick? I'm not disputing their cultural significance, but to continually hold up these and other classics as some of the greatest books of all time doesn’t' make much sense. Instead, I think these are just the books that are mentioned so much that the authors or titles stick in memory so even people who have never read any of them regard them as undisputed classics. On the other hand you have modern books, which for the most part just feature a lot of young adult dystopian bandwagon jumping. These books, like The Hunger Games and Divergent series won't hold a candle to some of the real science fiction classics, but have become global phenomenas tanks to Hollywood deals. It's a depressing state of affairs and not one that is going to change anytime soon I'm afraid.
The short answer here is that any book that has achieved a certain amount of success and hype will be seen as overrated by some people. It's just the nature of things and everything from Harry Potter to Fifty Shades of Gray will inevitably crop up I'm sure. Unless you are a hipster, stop worrying about what others thing is over or under rated and read what you want instead.
The most obvious answer would be books that are laughably bad, but captured the attention of public in such a way that they became bestsellers regardless. This would include the Twilight books as well as the Fifty Shades of Gray ones of course. There is very little to distinguish these books from all the other ones aimed at the same demographic, but once they became famous they just picked up momentum and kept going. They are a perfect example of books going "viral" and people jumping on the bandwagon just because they don't want to be seen as not being "with it."
Once upon a time, a man named Douglas Adams wrote a brilliant novel called Dirk Gently's Holistic Detective Agency. A few years later a British television series arrived that was inspired by this book and really rather good, even if it wasn't a direct adaptation of the book. It was promptly canceled after only a few episodes. Then a few years later BBC America took a stab at the license and created a new show based on the book. In typical American fashion they opted for over the top nonsense like secret CIA projects and slapstick humor to appeal to audiences. Unfortunately, this worked and the show continued for two miserable season before it was canceled. This makes Dirk Gently's Holistic Detective Agency the only book I know of that spawned both a great television show of the same name and a completely horrible one. I suggest you don't confuse the two.
All of the Harry Potter books by J. K. Rowling. For years I had to hear about how awesome the books are and how I must read them, but when I finally sat down and did so it was a letdown. For something that is supposed to be the best-selling book series in all of history, there are just too many plot holes and lazy writing to agree. It's no use trying to argue the point with Potter fans either as they are all so obsessed with the boy wizard that they can't see any wrong with the books.