an old chestnut老掉牙的故事。nut是果仁，chestnut就是讓你口水直流的慄子。如果是放了很久的慄子，肯定不會有人想吃吧？因此，an old chestnut（放了很久的慄子）就被引申為一個笑話或故事被講過太多次，變得沒有意思或不吸引人。
看看老外聊天時怎麼用an old chestnut：
Monica: Bruce is dull and talks about the same things every day.
Derek: There you go again! Those stories are old chestnuts to me.
Monica: But I would much rather hear something new.
Derek: Something new? Like what?
Monica: To be frank. I'd like to hear that you want to take me out on a date.
莫妮卡：布魯斯真的很沒意思，每天都在說相同的事情。
德裡克：你又來了！這些抱怨對我來說都是老掉牙了。
莫妮卡：但我期望你有些新的回應。
德裡克：新的回應？比如？
莫妮卡：坦白說，我比較希望你來邀我去約會呢。
an old chestnut例句精選：
It is an old chestnut, but a telling one.
這是一個很老套的笑話，但是卻很生。
Whether there's truth in it or not, I can't stand that old chestnut.
不管這裡面有沒有道理，我受不了那老掉牙的話。
拓展學習：
cliche 陳腔濫調
repetitive 重複的
stale 無新意的
novelty 創新
fall into a pattern 一成不變
out of date 落伍的
be weary of 對 感到厭倦