口くちを酸すっぱくする

expression, suru verb (irregular)

repeatedly admonish; tell over and over

Idiomatic expression, often used as 口を酸っぱくして言う, emphasizing the speaker's repeated, sometimes tiresome, warnings or advice.

• 母ははは私わたしに、勉べん強きょうしなさいと口くちを酸すっぱくして言いった。

  My mother repeatedly told me to study.