fly in the ointment /'ɒɪntm(ə)nt/

informal

fly是苍蝇，ointment是油膏或者药膏。可想而知小小的苍蝇掉进了一缸油膏里，可不是把好好的油膏全糟蹋了吗?由此可以推想fly in the ointment这个习惯用语必定指虽小却搅了全局的东西或事情。

a single thing or person that is spoiling a situation that could have been very positive or enjoyable

美中不足之处;令人扫兴的东西(或人)

I'm looking forward to Sunday, the only fly in the ointment being the fact that I'll have to sit next to my mother-in-law.

我期待着星期日的到来，唯一令人不快的是，到时我必须坐在丈母娘旁边。