"Boys, it seems our friend T-Bird won't be joining us tonight, on account of a slight case of death
." - Top Dollar, The Crow
When the villain needs to reveal that a character has died, but really doesn't want the death to overshadow how bad he is, he tosses out the news like a magazine he didn't particularly enjoy. Callous, often sarcastic, playful, and even lighthearted, this delivery also increases the emotional impact on those who have hearts.
Subtrope of Understatement
, owing its significance to the subject matter and the intense cognitive dissonance.
This is all we have so far; I know I've seen others. Do add what you can!