For me, it’s occasionally coming up when I listen to comedians. A year back I also heard a story about a white person who grew up poor, became financially stable with a good job, and then punched down and started calling other white people “white trash.”
To me it’s obvious this is poor-shaming. But I have a feeling it’s far more complex than that. I’m not even white and I feel degraded whenever I come across those words. I barely know what it means, but it breaks my heart anyways to hear.
As other poster have said the idea came about hundreds of years ago. It is part of a eugenics classiest idea that the upper class of society is of good breeding and the lower class is of bad breeding. Believes such as disease being created by the lower class where part of this. If you read old works like Lovecraft you will see base white trash referenced as a sort of devolved and lesser white person. White trash is the non confirming portion of the poor lower class that society was attempting to dispose of. Another poster referenced the book white trash which is about some of the history of class in early America.