So once he's done with the firstborn, Loki takes his friend Bartleby out for a post-slaughter drink. And over many rounds, they get into this discussion about whether or not murder in the name of God is okay. Now, Bartleby can run circles around Loki intellectually, not to mention that Loki's already half in the bag. And in the end, Bartleby convinces Loki to quit his position and take a lesser one that doesn't involve slaughter. So - very inebriated - Loki tells God he quits, throws down his fiery sword, and gives Him the finger. Which ruins it for the rest of us, because from that day forward, God decreed that all angels could no longer imbibe alcohol. Hence all the spitting.

Metatron