A "curate's egg" describes something that is at least partly bad, but has some arguably redeeming features.
In its original context, the term refers to something that is obviously and essentially bad, but is willfully described euphemistically as only partly bad—its supposed good features credited with undue redeeming power.
The term derives from a cartoon published in the humorous British magazine Punch on 9 November 1895. Drawn by George du Maurier and entitled True Humility, it pictures a timid-looking curate eating breakfast in his bishop's house. The bishop remarks with candid honesty to his lowly guest: "I'm afraid you've got a bad egg, Mr Jones." The curate replies, desperate not to offend his eminent host and ultimate employer: "Oh, no, my Lord, I assure you that parts of it are excellent!"
The cartoon relies on an objective analysis and intuitive understanding of the depicted scenario: a self-contained egg cannot be both partially spoiled and partially unspoiled. To pretend to find elements of freshness in a bad egg is thus a desperate attempt to find good in something that is irredeemably bad. The humour derives from the fact that, given the social situation, the timid curate is so obsessively fearful of offending that he cannot even agree with his superior's acknowledgement that he has served a bad egg, and thereby ends up looking absurd in his obsequiousness.
The final issue of Punch, published in 1992, reprinted the cartoon with the caption: Curate: This f***ing egg's off! Thus Punch drew a contrast with the modern era, implying that people have little care for niceties of Victorian over-stretched good manners towards those people then considered social superiors.
- "The past spring and summer season has seen much fluctuation. Like the curate's egg, it has been excellent in parts." (Minister's Gazette of Fashion, 1905)
- "All the same it is a curate's egg of a book. While the whole may be somewhat stale and addled, it would be unfair not to acknowledge the merits of some of its parts." (Oxford Magazine, 1962). 
- "Like the curate's egg, the details of Wegener's hypothesis were good in parts." (John Gribbin, The Scientists, 2001).
- "Fishman... attempted a 'systematization' of SWH [Sapir-Whorf Hypothesis], suggesting that its extreme versions were untenable..., but that, like the curate's egg, it was excellent in parts." (Philip K. Bock, "World view and language", in Encyclopedia of Linguistics, ed. William Bright, vol. 4, Oxford University Press, 1992, p. 250).
- Paraphrase of definition in Collins Dictionary of the English Language, London, 1986, p.381
-  Oxford Dictionaries definition]
-  Cambridge Dictionaries definition]
- The New Oxford Dictionary of English. Oxford University Press. 1998. p. 449.
- van den Bergh, Hubert (2013). How to Sound Really Clever: 600 Words You Need to Know. A & C Black. p. 39. ISBN 1408194856.