Dean and Sam in “Unfinished Business”

Dean

You know, I felt for those sons of bitches back there. Lifelong torture turns you into something like that.

Sam

You were in Hell, Dean. But maybe you did what you did there... but you're not them. They were barely human.

Dean

No, you're right. I wasn't like them. I was worse. They were animals, Sam. Defending territory. Me? I did it for the sheer pleasure.

Sam

What?

Dean

I enjoyed it, Sam. They took me off the rack, and I tortured souls, and I liked it. All those years; all that pain. Finally getting to deal some out yourself... I didn't care who they put in front of me, because that-that pain I felt, it just slipped away. No matter how many people I save, I can't change that. I can't fill this hole. Not ever.