adj: really, really bad.
Taken from the book 1984, where language is disintegrating, people build words using smaller words. The make-up of this word is as follows:
doubleplus - as opposed to just 'plus', which would mean 'really'
ungood - opposite of 'good', or 'bad'
That movie was doubleplusungood, it was horrible!
It means very bad! Like, REALLY bad!
Jimmy thought the movie was doubleplusungood, since it starred Ben Affleck.