Totally spoiler-free Reason #83 why I'll never be on the writing team for Supernatural:

I would have pitched a mid-season reveal that Castiel and Ruby have secretly -- suprise! -- been in cahoots all along, spying on the brothers and devising nefarious schemes, as the Boris and Natasha of the apocalypse.

By which I mean -- and would illustrate through the power of flashbacks! -- that they actually use Boris and Natasha as codenames and terms of endearment for each other. And naturally they'd speak in cartoonish Russian accents during their illicit rendezvous. No doubt at different points, Ruby confuses Sam and Castiel baffles Dean when they each accidentally lapse into the Russian accents but unfortunately the brothers don't compare notes until it's too late. Nor does it help that the Winchesters somehow never see through the outrageously transparent disguises that Ruby and Castiel adopt.

Of course Castiel and Ruby would contemptuously refer to the Winchester brothers as "moose and squirrel." And when their treachery is finally revealed, Sam and Dean will fight over which one of them is Rocky to the other's Bullwinkle.

...I swear it sounded great in my head....