Even worse than that was the moment where he breaks down in the Winchester basement. "I couldn't save any of them!" Just for a second he's way over the Despair Event Horizon, and he just thinks this caps off all the failures in his life...damn, Simon Pegg needs an award for that scene.
Liz: How many we got left?
Shaun: Two. S'pose we could take a few of 'em out if they stood in a line.