Fruitcake

wiktionary

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From fruit +‎ cake, 1854. Sense of crazy person, 1952 (predated by nutty as a fruitcake, 1914).

etymonline

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fruitcake (n.)

also fruit-cake, 1838 in the literal sense "a rich, sweet cake containing fruit," from fruit + cake (n.). Slang meaning "lunatic person" is first attested 1952.