I was reading Easy by Tammara Webber, and I really did not like it. I did not like the plot. I did not like most of the characters. It's not like the writing was amazing either, but even though I did not like it at all, I still wouldn't say it's a bad book. The only reason I would call a book bad is if they are demeaning of groups of people (i.e. sexism, racism, etc.). However if these aspects are used in the plot that is a different story. If the book is set in a world with slavery still there is obviously most likely going to be racism in the book, but that is very different from a character making racist remarks just because. If it's not used to drive the plot, those are things that make a bad book because they can encourage those negative stereotypes.
Sorry for that mini tangent. Back to the actual topic at hand. I believe that when I don't like a book that doesn't make it a bad book. I just think that that book is not for me at this point in my life. Books like Twilight and 50 Shades of Grey are called bad books rather regularly, and while I think neither of them are great pieces of literature. If you take them at face value, it's just a story. Now if you look deep they have some bad messages, as do most books, but there are always some selling points.
I just think that a lot of books that we label as bad just aren't books that are necessarily for us. I am not going to enjoy a lengthy classic because that's not something that is for us. While broadening our horizons is a good thing, I think some genres of books or authors aren't for us. This made me realize that new adult isn't a genre for me right now, but maybe some day I'll find something I really enjoy. However with that said I don't think Easy was a bad book it just wasn't for me because while you may dislike a book there is always someone else who loves it, and I don't think it's anyone's place to tell someone that a book they enjoy is a "bad book".
Those are just my thoughts and opinions.