Baby looks at the two of them blankly, a complete lack of comprehension on his features. He wants to listen to Dean and have Dean call him by his proper name, which would make both of them happy, but he honestly has no idea what they're talking about.

Clothes? What clothes? Cars don't have clothes. Do they want him to take off his paint? HE CAN'T TAKE OFF HIS PAINT. HE'S SUCH AN UGLY GREY COLOR UNDERNEATH.

So, he covers his body with his hands like they're some kind of creepy, old perverts and looks absolutely aghast.