The sentence was "オレが口を酸っぱくして教えたよね？"
To my understanding, it means "Did I teach you to do it with a sour mouth?" or actually, "Didn't I teach you with a sour mouth?", but I'm not sure what sour mouth means.
口を酸っぱくして教える means "tell [somebody something] over and over again [without any effect]". 教える here is "tell" rather than "teach". A corresponding English idiom would be "I've told you till I'm blue in the face!" I imagine the underlying meaning is "I've said this so many times I've got a sour taste in my mouth".