The “curate’s egg” has its origin in Victorian-era humour, which can sound rather dull to modern ears. The humour often incorporated themes related to social and class divisions prevalent during the period. This is evident in the “curate’s egg”, which started as an obscure clerical anecdote and then reached a wider audience through two cartoons published in 1895.

The second of these cartoons, shown in the accompanying picture, appeared in the widely circulated “Punch” magazine of 9 November 1895, and is the version that has become a meme. The setting is the rigid hierarchy that then existed within the Church of England. Mr Jones, a curate (someone on the lowest rung in the church organisation) has been invited to breakfast with the Bishop (an exalted rank). All has not gone well in the kitchen and the timid Mr Jones is in the embarrassing situation of being presented with an inedible breakfast, but not knowing what to say. The cartoon appeared with this dialogue:

Bishop: "I'm afraid you've got a bad egg, Mr Jones!"

Curate: "Oh no, my Lord, I assure you! Parts of it are excellent!"

Anyone who has had a rotten egg, cooked in any style, will know just how horrible it is and will understand the poor curate’s effort to find a polite way out of a really bad situation, by saying that the egg has good and bad points.

The expression is used today as a description of something that is partly (or mainly) bad but partly good, taking the curate’s words at their face value.

More Info: en.wikipedia.org