in one ear and out the other

Essentially ignored, dismissed, or forgotten almost immediately after being heard (as of something spoken). My instructions to my kids are often in one ear and out the other, especially if they have their phone in front of them. I have to remind my students a dozen times to copy down their homework—it's like in one ear and out other. You can try to convince him, but with him it's usually in one ear and out the other.

Prov. heard but not remembered. (Used to describe something that someone does not listen to.) Ellen: Did you tell Junior to be careful with the car when he drives it? Fred: Yes, but I think it went in one ear and out the other. The teacher felt that everything she told her students was in one ear and out the other.

Quickly forgotten, as in Their advice to her just went in one ear and out the other. This expression, a proverb in John Heywood's 1546 collection, conjures up a graphic image of sound traveling through one's head. [Late 1300s]

Without any influence or effect; unheeded: His mind was made up, so my arguments went in one ear and out the other.

Inattentive; soon forgotten. This vivid image dates from Roman times. “The things he says flow right through the ears,” wrote Quintillian (Institutionis Oratoriae, ca. a.d. 80). The sentiment was echoed by Chaucer and joined John Heywood’s 1546 proverb collection (“Went in the tone eare, and out at the tother”). Thomas Hood punned on it in his “Ode to the Late Lord Mayor” (1825): “He comes in at one year, to go out by the other!”