Koban is a small oval-shaped gold coin which circulated in Japan prior to the Meiji Restoration of 1868. The expression is used when suggesting that not everyone can appreciate an object to the same degree. Similar to “do not cast pearls before swine”, it means “don’t offer anything of value and merit to those who are incapable of appreciating it.”
A: Sasaki-san no tokoro ne, musukosan no tame ni gurando piano o katta n da tte. Demo musukosan wa ongaku ni wa mattoku kyoomi ga nai mitai yo. Neko ni koban to wo ano koto ne.
A: I hear that Sasaki bought a grand piano for his son, but the son isn’t interested in music at all. That is truly a case of “pearls before swine,” isn’t it?