lose one's marbles . lose one's marbles {v. phr.} To go mad; become crazed. Stan must have lost his marbles; he is hopelessly pursuing a happily married woman. Categories: add yours {v. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: L Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Leave my opinion