What is a deal breaker for you in a book? For example, do you abhor love triangles? Or can't deal with bad editing?
The deal breaker for me is when I cannot relate to the main character in anyway. If there isn't a connection I can't continue on, because the entire time I am just complaining to myself about how awful this main character is and everything he/she does I judge and criticize. If I can't understand where a character is coming from or why they are doing what they are doing then why would I bother wasting my time reading it, when I am just getting angry the whole time? Bad editing is another thing that irks me, but it has never stopped me from reading the book.