curate's egg

Etymology
From a cartoon by the Franco-British cartoonist and author (1834–1896) captioned “True Humility” in the 9 November 1895 issue of Punch magazine, in which a bishop says to his mealtime guest, a curate, “I’m afraid you’ve got a bad egg, Mr. Jones!” The timid curate replies, “Oh no, my Lord, I assure you! Parts of it are excellent!”.

Noun

 * 1)  A thing which has good and bad parts, but is overall spoiled by the bad.

Translations

 * Welsh: ŵy'r curad