"Dirty Mouth, clean it up with Orbit gum"

I feel that books should use what is necessary to portray the scene they want to portray.  I do not think that there is a line between what is appropriate and what is not because if the book has words that are too much for a person to handle they should not read the book, they do have that choice.  The word choice is that of the authors and reader's can deal with this by putting themselves into the novel and using the words as just part of the context of the story.  I think author's choose to use these words because they add more reality into the writing and make the story show emotion more as well.