At first, it's only a flash of pink, inching up past the waistband of Dean's jeans as he climbs out of the car. Only a flash, but Castiel feels it like a burn, the impact of that sliver of silk crashing into him like a wave even as Dean's shirt falls back into place to cover it, Dean's back turned towards the car as he heads off for gas. Castiel knows a lot about Dean, his secret hopes and long-hidden anxieties, but the idea that he might routinely drive around with nothing but silk between the heft of his dick and the heavy-duty denim of his jeans is new and shocking, makes Castiel's skin prickle hotly. Dean - big, macho Dean - is out there right now, in public, in women's underwear, secret under his jeans, and Castiel doesn't know why but he does know one thing, and that is that he wants more than anything to see what those panties look like stretched over Dean's cock.