耳にタコができる literally means “to get a callus on your ear” and we use this expression when we keep hearing the same thing over and over and over again.
Of course, we don’t usually get calluses in our the ears, but thinking about how calluses are formed, from the same action being repeated over and over, we can see the connection 耳にタコができる is trying to create here. If you are an experienced Japanese speaker, you may have seen the word タコ used in other words or sentences to mean “octopus” - but it’s not! We definitely don’t have octopuses in our ears - タコ (or sometimes written in hiragana as たこ) is also used as a casual way to say “callus.”
耳にタコができる has a bit of a negative connotation, which is that annoyed feeling you get when you’ve heard the same thing enough. So please be careful when you use it! 耳にタコができる itself works as a verb. And since it’s just a metaphor, we often combine this expression with ～ぐらい or ～ほど which we use in Japanese to express the degree or extent of something.
I’ve heard the same story enough times!
I am constantly telling my kids that they should study more.