Blue Nun, Black Tower, generic 'Liebfraumilch', V.P., 'British Wine', there were some truly awful things about, probably still are if you go looking.
The nastiest I ever tasted was the Bulgarian white wine I got in a hotel duty free shop back in '79. I was hotel-bound due to an injury and went to get a pack of cards to play patience, and a half-bottle of brandy. As the shop only took hard currency I offered my smallest note, a £5. My change was a tube of Primula cheese, some Dutch Guilders, and three bottles of supposed wine which I reckon started life in the battery of a malfunctioning tractor. It was dirt cheap, but still a bad bargain.