Brought on by the wee one selling Girl Scout cookies tonight.

Castiel has a thing for citrus flavors. Someone, somewhere introduces him to Lemonades... delicious shortbread cookies with lemon frosting on the undersides. Once he discovers where these cookies come from and how to procure them for himself, Castiel makes it a point never to pass by a Girl Scout selling cookies so he can snag a box of Lemonades.

And he rarely shares. If you get a Lemonade from Castiel, that's like getting a phoenix to give you one of its feathers.

I can just see him sitting in the back of the Impala, blissfully munching his cookies until Sam turns around to look at him. And then for a split second he mentally mantles over the box in his lap until it's obvious that Sam doesn't want to take his cookies.

Sam cottons on, of course, and does it occasionally just for the face Castiel makes at him when he does it.

Bonus headcanon: Castiel tries to give the Winchesters cookies from the back seat to make them stop fighting.