The high school in Denver, Colorado, where two social outcasts, who were utterly and wholesomely sick of their bullying by the Cool Jocks and similar, went on a murderous rampage. Not that this was justified, but one can see why they did it - it wasn't Marilyn Manson, it wasn't The Matrix, it wasn't Neo-Nazism, and it wasn't Quake. IT WAS SOCIAL CONDITIONING. They had been led to believe by those at the school that their lives were worthless, so they thought, "Mise well take a few down on our way out!".
Of course, these two individuals are dead now, so we can't question them as to their real motives.