Sam and Dean in “Unfinished Business”

Sam

Says who? Look, I'll work this damn case, but you lied to me, and you killed my friend.

Dean

No, I put down a monster who killed four people, and if you didn't know her, you'd have done the same thing.

Sam

I did know her, Dean.

Dean

Yeah, which is why you couldn't do it. Look, I get it. There are certain people in this world, no matter how dangerous they are, you just can't.

Sam

Don't pull that card! That's bull. Look, if I've learned one thing, it's that if something feels wrong, it probably is!

Dean

Usually, yeah. But killing Amy was not wrong. You couldn't do it, so I did. That's what family does -- the dirty work. And I woulda told you, eventually, once I knew that this whole "waving a gun at Satan" thing was a one-time show. I think it's reasonable to want to know that you're off the friggin' high dive, Sam. You almost got us both killed, so you can be pissed all you want, but quit being a bitch.