expression
fed up with hearing something repeatedly
Abbreviation of 耳に胼胝ができる (literally 'to get a callus on one's ear'). Used when someone has heard the same thing so often that they are sick of it. Colloquial and idiomatic.
See also: 耳に胼胝ができる (みみにたこができる)
「勉強しなさい」って耳タコだよ。
I'm fed up with hearing 'Study!' all the time.
その話はもう耳タコだから、やめてくれ。
I've heard that story so many times I'm sick of it, so please stop.
The full idiomatic expression from which 耳タコ is abbreviated. 耳タコ is more casual and clipped.
Clipped form of the idiom 耳に胼胝ができる (to get a callus on one's ear), implying that hearing the same thing repeatedly is as irritating as a physical callus.