foam at the mouth . foam at the mouth {v. phr.}, {slang} To be very angry, like a mad dog. By the time Uncle Henry had the third flat tire he was really foaming at the mouth. Categories: add yours time {slang} {v. phr.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: F Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Add my comment