Well I have heard the term 'river rat' far too many times while residing in cheatham county. You are correct it isn't so much income as it is perceived income. But the prejudice does exist. I have lived in three entirely different parts of that county (petway road (x2), river road, ashland city (x2)) and it is almost like having three different dialects. I guess living in clarksville (x2) is the closest I came to living in north cheatham.
I am a firm believer of letting the play on the field doing the talking.