if you keep your mouth shut, you won't put your foot in it

If you keep quiet, then you won't unintentionally say something foolish, tactless, or offensive. A: "I just congratulated Sarah's sister on being pregnant. She isn't." B: "Oh, man, that's embarrassing. You know, if you keep your mouth shut, you won't put your foot in it." A: "Look, just let me do the talking in court, OK?" b: "Why?" A: "If you keep your mouth shut, you won't put your foot in it." A: "Look, I wasn't trying to be offensive, but what I meant was—" B: "Tom, you're just making it worse. If you keep your mouth shut, you won't put your foot in it."