Say something foolish, embarrassing, or tactless. For example, Jane put her foot in her mouth when she called him by her first husband's name. This notion is sometimes put as having
foot-in-mouth disease, as in He has a bad case of foot-in-mouth disease, always making some tactless remark. The first expression dates from about 1900. The variant, dating from the mid-1900s, is a play on the foot-and-mouth (sometimes called hoof-and-mouth) disease that afflicts cattle, causing eruptions to break out around the mouth and hoofs.