Well, for one, many writers and aspiring writers get angry that Stephenie Meyer took the prescious abstract that is twilight to title her book after, despite that there would be many more fitting titles for it.
There's kind of an unwritten rule in the literary world, you don't claim concepts like that. Of course, Stephenie Meyer pretty much ignored anything literate, but anyways.
The publicity.
Most of the people who hate it have nothing against the book/movie itself, but despise the millions of annoying, idiotic 12-yr-old Edward fangirls who probably never even READ the book.
And then there's the environmentalists, who are angry about how much trees are being wasted on the 1000+ pages of nothing that is each copy of the twilight series.
Shall I go on?