not happen (/seen) once in a hundred years (/a century) ? 不是要開(kāi)會(huì)嗎？ ～的事，…… (《老舍劇作選·龍須溝》 62) Have you forgotten the meetings today! This is something that doesn’t happen once in a hundred years.
百年不遇bǎi nián bù yù
形容很難遇到。very rare occasions,rarely meet in a century