-The entire premise surrounding a short, lesser known series called Chainsaw Saitama Shoujo. Long story short a girl is in a relationship with a guy she's completely head over heels for. She then sees him in the arms of a new girl , shows up with a chainsaw at school the next day and proceeds to massacre her classmates.... It's played off for dark humor in some aspects but still kind of a sick story
-Black Butler-
Ciel ordering Sebation to,
Spoiler (mouse over to view)
Kill a bunch of orphans, and then acting as if it was the right thing to do