This idiom has been used in the title of some books: The Fly in the Ointment: 70 Fascinating Commentaries on the Science of Everyday Life by Joseph A. Schwarcz and The Fly in the Ointment by Alice Thomas Ellis.
Fly | fly | North Fly District | Fly My Pretties | Tsetse fly | North Fly district | Iraqi no-fly zones | Gonna Fly Now | Fly FM | fly fishing | Horse-fly | Fly to the Sky | Fly River | Fly fishing | Federation of Fly Fishers | Common green bottle fly | Supa Dupa Fly | Stable fly | Fly, Robin, Fly | The Stinging Fly | Learn to Fly | Fly Over States | Bill Gates' flower fly | William Fly | Where the Bullets Fly | warble fly | Velcro Fly | Turtles Can Fly | The Rain (Supa Dupa Fly) | The Flying Fruit Fly Circus |