Green’s Dictionary of Slang

1. a worn-out, useless car, occas. aeroplane (see cit. 1942).

1942		C.R. Bond 4 Mar. in A Flying Tiger’s Diary (1984) 122: Newkirk’s Second Squadron swapped a couple of good P-40s for our two clunkers.
1950		Associated Press 18 Feb. n.p.: Before you sell a clunker [an old car] to the junkman [...] smash the transmission [W&F].
1954		(con. 1940) C. Chessman Cell 2455 179: I can dump this clunker as soon as we can get hold of my car.
1962		D. Dempsey ‘Lang. of Traffic Policemen’ in AS XXXVII:4 267: bucket of bolts, n. phr. klunker, n. An old rattletrap car or truck.
1964		The Beach Boys ‘This Car of Mine’ 🎵 Thought I could tell / Under the coat of rust she was gold, / No clunker.
1978		A. Maupin Tales of the City (1984) 76: The parking lot [...] was jammed with vehicles: flowered hippie vans, city clunkers, organic pickups.
1983		S. King Christine 31: That old clunker of a car. [Ibid.] 33: You’ll need every penny of it before you’re through with that clunk.
2002		Church of the Ressurection 22 Mar. 🌐 How many of us treat our spiritual journey like we are driving a cheap, old klunker on a neglected country road?
2003		Mad mag. Jan. 18: We drove to Mexico City in his old clunker.
2017		T. Pluck Bad Boy Boogie [ebook] ‘You want me to show you how to handle that old clunker of yours?’ Ramona said. ‘We can’t all have James Bond cars’.

2. anything useless, unattractive, incompetent.

1949		F. Brown Dead Ringer 172: Don’t jump into this, Rita. You might be buying a clunker.
1960, 1975		Wentworth & Flexner DAS.
1971		L. Bangs in Psychotic Reactions (1988) 14: I believe that record – no, the whole band, that’s right – is one of the all-time clunkers of history.
1989		H. Rawson Dict. of Invective (1991) 47: clunkhead. Popularized by Arthur Godfrey on radio and television in the early 1950s (Dictionary of American Slang, 1975); possibly from clunker, for anything that is old, beat-up, and doesn’t work well.
1995		C. Hiaasen Stormy Weather 238: Morganna — what a clunker of a name to remember in the heat of passion!
2000		T. Blacker Kill Your Darlings 158: A list of titles, including such clonkers as Terpischore of Life [...] was drawn up.
2000		Indep. on Sun. 5 Mar. 21: Perhaps it’s a hangover from that old Leon Uris clunker Exodus.
2000		R.G. Barrett Leaving Bondi (2013) [ebook] [A]nybody that would invest money in a clunker like Leaving Bondi would have shit for brains.