I've got this little plot idea in my head, where TFW go on vacation, and Dean says to Cas smth like "No, you're not going to a beach resort in a suit" so he makes Cas wear his clothes. Cas does what his friend says, though he doesn't understand, what's wrong with his trenchcoat.
Well... This decision had a much more unexpected result for Dean... Who knew, what Cas was hiding under all these layers.