fly in the ointment

(idiom) a minor problem that spoils something

Example Sentences:

A: Did you have a good day at the beach?
B: It was all right. There was a fly in the ointment, though. Some teenagers there were being noisy.
A: I hate teenagers!

The only fly in the ointment during our whole vacation was when our flight was delayed.

Media:

Similar idioms:

1. go fly a kite
2. when pigs fly
3. fly in the face of
4. coach