To hear the same thing so often that one becomes fed up — literally 'get calluses on one's ears.' Used to mean being tired of hearing something.
上司に同じ注意を何度もされて、もう耳にタコができた。
My boss scolded me the same way so many times that I'm sick of hearing it.
その曲はラジオで何度も流れて耳にタコができるほどだ。
That song is played on the radio so often it's gotten on my nerves.
『早く寝なさい』と親に言われて耳にタコができている子どももいる。
Some children are so used to being told 'go to bed early' they've grown tired of hearing it.
説明を何度も受けて耳にタコができたが、まだ理解できない部分がある。
I was told the explanation so many times I was fed up, yet there are still parts I don't understand.