I heard a misconception that you can write with improper grammar to represent a character that has improper grammar. What you really want to do is use proper grammar to help set the tone of a character that is unable to use proper grammar or to represent a theme of ignorance. Quoting a character who says something with flawed grammar is not considered grammatically inappropriate as those quotes are merely representative and are not "actual" writing.
Fight Club has questionable grammar in it's novel, but it helps for falling into the headspace of the narrator's spazzy hyperactivity. It works well for unreliable narration, and if the piece of work jumps between different characters it can help for establishing a tone shift.
Sure, it's just that writing style is not the exact same as representing tone. They both arrive at similar results and are both displaying information to be interpreted.