The first time I came across the term was in Harper Lee's "To Kill a Mockingbird", referring to poor and uneducated whites who had addiction issues and who behaved in criminal ways that damaged themselves and others around them. I'm not sure if the meaning has changed since then.
Maybe "trash" refers to the way people who live this way are ignored and discarded by most of mainstream society. It's a prejudicial word because it ignores the stresses and trauma produced by poverty, malnutrition and lack of education - which in many ways literally cause the addictions, violence and crime. I'm not saying the stresses of poverty and ignorance are the sole cause - but they are major contributors.
It's the radically different in places like Scandinavia, Greenland and Portugal, where free and good quality education ensures that more people hold good jobs, where free medicine fixes most health issues before they become serious and expensive, and where criminal ricidivism is only 20% (compared to 80% in America & countries without a sufficient social safety net). Sure, the taxes are high, but the happiness and wellness indexes, and average living standards are far higher.
I think it’s a very rude and hateful thing to say about people.. ironically the people I've seen use it were not any much better than the people they directed it at 🙄 it seems uncalled for imo .. tho i have seen some really trashy people like literally trashy but why be racist about it? seems extra hateful 😳
I really don’t like the idea of anyone being called "trash" because of things like income level, upbringing, stuff beyond their control. I have a special take on that particular term, since no one generally refers to different classes of other groups as "trash".