What's the gloomiest and most morbidly obscene and darkest idea you've ever thought of?

What is the darkest thing you have ever thought about? What's the darkest thought you had ever pop up in your head? What is the most inappropriate thought you've ever had?
OK, fine! When people stand to close to me I think "I could totally kiss them right now." But not just sexy people, teachers and old people and stuff. Ugh. What is the single worst idea you've had that you thought was brilliant at the time? What's the darkest realization you've ever come to?