There are several synonyms for the phrase "frown at." One word that comes to mind is "scowl," which refers to a facial expression that conveys disapproval or dissatisfaction. Another synonym is "glower," which describes a more intense and menacing form of scowling. "Grimace" is another option, which refers to a contorted expression that can indicate pain or discomfort, but can also be used to convey dislike. "Sneer" is a synonym that implies contempt or derision, while "arch" suggests a raised eyebrow or expression of skepticism. Whatever word you choose, all convey a negative or disapproving attitude towards something or someone.