Is there a spanish esp. mexican for people who sit on their asses and don't work (the poor ones not the rich ones)?

You are getting Spanish words for "lazy," not for some equivalent to "white trash."

Among Mexicans, "cholo" is the closest thing I can think of that means "Mexican trash." It is used by hard-working Mexican immigrants to refer to ghetto Mexican-Americans living on welfare.

In Mexico they are called nacos and in Brazil, Caipiras.

Look for "redneck in other countries" in google.

"Un manta y borracho"--- lazy bum

In Ecuador you would say:

Caimán—Lazy person or Calzonazo—Lazy man

In Spain: “un huevón / una huevona” – lazy person / layabout (derogatory)

In Puerto Rico you might say: "Bambalan” – Lazy Bum

Pues si amigo!

I suppose you could say "un perezoso" (a layabout).