You're a familiar. Dean's familiar to be exact. Which is strange because he is neither a witch nor a warlock.

Your familiar form, a dog. A beautiful fully grown pure blooded German Sheppard.

And Dean hates dogs.

One night, in the bunker, Dean was sitting on the couch. Sipping a beer and watching some crappy TV show. You came up in all of your doggy glory and nuzzled against his legs, laying down at his feet.

He really does hate dogs.