fly in the ointment 美中不足的事

說明：

fly 是名詞，指小蟲、蒼蠅。可依據語法在 fly 前面加上 a 或 the。ointment 是膏油。以前膏油是貴重之物，中間發現了蒼蠅，實在是件憾事。這個說法和廣東話的「一粒老鼠屎，攪和一窩粥」相似。原典出自〈傳道書〉第十章第一節：「死蒼蠅，使作香的膏油發出臭氣。」

例子：

I was told the party was wonderful last night. But I was dead tired and I slept through it. That was really a fly in the ointment.

by Thomas Shum