Green’s Dictionary of Slang

1. a fool, a dolt, an incompetent.

1951

Edson ‘The Gumps’ 13 Aug. [synd. comic strip] Tell one of those clunkers [golfers] what a great stroke he has, and he’d vote for you [W&F].

2. (US) a blunder, a mistake.

1999

Observer Screen 4 July 6: The system produced it’s fair share of clunkers but at least they tried, OK? They weren’t high-concept clunkers.