The young are always a good target for insults. They don’t vote, they’re impatient and stupid! 
I use this term and I find it pretty fitting.
Let me give you a little background. I’m from Ohio originally, but I now live in California. I have friends from all different backgrounds, from all over the world. I know some people who are so dirt poor they’ve eaten cat for lack of any other meat.
White Trash and Trailer Trash are synonyms for me, and the people I’ve considered White/Trailer trash sometimes are non-white and sometimes live in houses. I just know no other term for what to call that group of people.
I have known quite a bit of trailer trash people in my day. When I was in grade school, the only friends (and boyfriend) I had were from trailer trash families. Trailer trash children I love and adore and I have several friends and family who are trailer trash and I care for them deeply (and try to help out of their situation) but the parents make me so angry and sometimes I just want to give them a kick to the head. The children are never responsible for the situation and often the children have to be the adults in the family and not only care and clean for themselves but also care for their younger siblings.
White/Trailer Trash people often live the way they do because the parents are heavily involved in drugs. The houses are FILTHY and they can’t manage to take care of their kids on their own. Often the responsiblity for child care falls on other people which is one of the reason I get so angry at them.
My 80 year-old grandpa somehow manages to care for 3 children that my nearly worthless uncle and his completely worthless girlfriend had. The house they share is overcrowded with 7+ people living in a 3 bedroom that has 1 working bathroom. Not all of them are white, some are Mexican or half-Mexican. I have been going over and cleaning out the house whenever I have a chance, but things are just so dirty and there is just so much junk that I don’t think I’ll ever manage to get it to a level where it would be even close to ‘okay.’ My uncle’s girlfriend has taken so many drugs that her brain is completely fried. She does nothing but sit around the house, eat, sleep and go into a rage when we mess with ‘her stuff.’ Which just makes trying to clean things difficult. My Uncle at least tries caring for the children, (they get a lot of love, but always have dirty clothes and are under fed) but he hasn’t had a job and has been in and out of jail almost all his life. When my grandpa dies, the children will probably be taken away by the state.
I have friends and I’ve dated people who lived in messy houses, but their parents worked and my friends worked and went to school to try and help out the family. I don’t regard those people as white/trailer trash.
I do think the term is not a very fitting one, I’ve known several people I would consider white/trailer trash that weren’t white and didn’t live in trailers. But there is no other term to refer to people basically live off other people in that way. I’ve noted that the term ‘white trash’ was used more in almost all-white Ohio while ‘trailer trash’ is more common out here in multi-cultural California. The white trash people I knew in Ohio were racist, so that might have something to do with the term.
I think if you make fun of black people then you are making fun of every black person. But “white trash” signals that you are not talking about the bad white people. I think it is clear when you say white trash that you mean stupid white people.
No one really considers themselves white trash. Lots of people consider themselves black.