1
general::
Phrase(s): in (at) one ear and out (of) 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.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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]
American Heritage Idioms