Phrase to be used when someone delivers bad news in an otherwise pleasant conversation or time. It comes from the idea that Morrissey (solo artist and frontman of The Smiths) wrote depressing lyrics which were then often juxtaposed with quite upbeat or happy music. For example the song "Girlfriend in a Coma" or the chorus lyrics to "There is a Light that never comes out"
Dave - "My wife is pregnant, I'm going to be a father!"
Sally - "That's awesome, congratulations Dave!"
Steve - "The baby might be born with a disability"