I have used, and heard used, the word "plonk" to mean "cheap wine", as in "two buck chuck" (although I understand that 2BC is a specific cheap wine).
However, in perusing a Spanish/English dictionary, I came across an entry saying that "plonk" is English for wine, with no notation of quality. Well, hmmmm..
So I went to my dictionary of slang and found the same thing... it comes from Austrailia/NewZealand in the early part of the 20th century. It started out meaning "cheap port", and by extension, =any= wine. By 1975 the beatniks used it for any cheap and readily available alcoholic drink. But nowhere does it mention "cheap wine" as its own sense of meaning.
So... how do you folks use the term?
Jose