fruitcake

1 a person judged to be legally or medically insane some fruitcake who insisted that he was an alien from another planet Synonyms bug, crackbrain, crazy, fool, lunatic, head case, loon, loony, maniac, nut, nutcase, nutter [British slang], psycho, psychopath, sickie, sicko, wacko (also whacko)Related Words madman, madwoman; abnormal, deviant; manic-depressive, monomaniac, mythomaniac, neurotic, obsessive, obsessive-compulsive, paranoid, psychoneurotic, psychotic, schizo, schizoid, schizophrene, schizophrenic, sociopath; character, codger, crack, crackpot, crank, eccentric, fantastic (also fantastical), flake, kook, oddball, oddity, original, quiz, screwball, tyke (also tike) [chiefly British], weirdo, zany; case, patient

2 a person of odd or whimsical habits the reclusive scientist has been called a loose cannon and a fruitcake by his detractors Synonyms character, codger, crack, crackbrain, crackpot, crank, flake, eccentric, head case, kook, nut, nutcase, nutter [British slang], oddball, oddity, original, quiz, screwball, weirdo, zanyRelated Words bohemian, maverick, nonconformist, quixote; coot, geezer; curio, rarity; freak; fantast, fantasticoNear Antonyms conformer, conformist, follower, sheep