Hello there, Cupid! The brothers and Castiel are greeted by Cupid on the episode "My Bloody Valentine." It's funny stuff.
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Supernatural Season 5 Episode 14 Quotes

Dean: Where am I going?
Sam: Dean, it's Valentine Day. Your favorite holiday, remember? I mean, what do you always call it - uh, Unattached Drifter Christmas?

Castiel: This is their handshake.
Dean: I don't like it.
Castiel: No one likes it.