Even in dialogue, your own style rules your selection. Do not give yourself a blank check of this kind: 'I'll merely reproduce what I think a character like so-and-so would say.' You have to reproduce it in the way your literary premises dictate.
Ayn RandThe age of the skyscraper is gone. This is the age of the housing project. Which is always a prelude to the age of the cave.
Ayn Rand