[Insert tofu joke here]
Literally: horse – ear – east – wind
Alternately: When a person utterly fails to heed what others have to say. Opinions, criticism, and so on just go in one ear and out the other.
Notes: This compound comes to us from the poetry of Tang dynasty poet Li Bai. The image appears to be a contrast between human enjoyment of a spring breeze (which for Li Bai blew from the east) while horses were unimpressed. It also seems likely that he was complaining about how people with no taste remained unmoved by his poetry!