不知所云: do not know what oneself (self deprecatory) or others are talking about; incomprehensible; be unintelligible; between the devil and the deep sea; be unable to make out what sb. is driving
言不由衷: talk insincerely; a left-handed compliment; be insincere in one's words [speech]; not to say what one thinks in one's mind; not to speak honestly; one's heart is far from one's lips.; one'