对牛弹琴 (duì niú tán qín)

Literally: Playing the lute to a cow

Example: “跟他讲古典音乐，简直是对牛弹琴。” — Talking to him about classical music is like talking to a brick wall.

English equivalent: Like talking to a brick wall

Origin: From the Mouzi Lihuo Lun (Mouzi's Treatise on Settling Doubts, late 2nd century): the musician Gongming Yi played a refined tune on the zither to an ox, which went on grazing. When he played sounds like a mosquito's hum and a calf's bleat, the ox pricked up its ears. Playing the zither to an ox is addressing someone who cannot understand.