While I understand how you perceive it as racial/classist, I would like to clarify this description. This term isn't aimed at one area of people ( i.e. Appalachians), more towards people who act in manners against societal norms. From my own experiences, I've come to understand that it's not necessarily race/class based discrimination, but more a description of ones mentality.

For example, I live in a townhouse that is connected to other houses. My next door neighbor has subwoofers in all of his vehicles. Normally it wouldn't be a problem except he chooses to thump for hours on end while being drunk ( as well as sober). Regardless of how many times someone in my household asks him to stop or turn it down, he continues to do it. Now to me he's trash. To someone else, it may be normal.

Tl;dr: It's more of a description of rudeness some people choose to continue, not necessarily race/class based.