…I’ve told you so many times that life gave me lemons. In my face.

口が酸っぱくなるほど
(kuchi ga suppaku naru hodo; “until the mouth turns sour”)

Definition:

Repeating oneself over and over. Saying the same thing ad nauseum. Often used to express exasperation at having to give the same warning or advice again and again without the message ever taking root. Generally followed by a verb indicating speech.

Breakdown:

Today’s kotowaza is a dependent clause. It technically contains a complete sentence, with subject and verb, but ends with a particle, implying that it is meant to be connected to something else that follows.

We begin with the noun 口 (kuchi), “mouth,” with the subject-marker particle が (ga). Next we get the adjective 酸っぱい (suppai), “sour” or “acidic,” in an adverbial form. This connects to the verb なる (naru), “become.” And finally we get the particle ほど (hodo), which indicates an amount, limit, or degree.

Notes:

A quick Google search for this phrase turns of lots of results from Japanese people wondering why the mouth is said to become “sour,” given that they’d expect it to simply dry out. The answer seems to be that in extreme circumstances, bacteria living in the mouth might be able to overcome the ability of one’s saliva to keep itself pH-balanced, leading to an acidic taste. Interestingly, the respondent to these questions seem to generally disavow ever having had such an experience themselves. It might simply be rare, or it might be that the origin or persistence of this idiom is based less on science than on the thematic appropriateness of sourness.

Example sentence:

「フライパンを素手で掴んだの？口が酸っぱくなるほど注意したのに、まったく」

(“Furaipan wo sude de tsukanda no? Kuchi ga suppaku naru hodo chuui shita no ni, mattaku.”)

[“You grabbed the frying pan with your bare hand? Seriously; I’ve warned you about that so many times!”]