Sam knows it’s blasphemous that he’s riding his brother’s cock in the backseat of his car.
Sam knows it’s blasphemous that he’s always had a thing for men of the cloth, that he felt compelled to finger himself after an Easter service he begged Dean to take him to. The crisp black clothing, the white collar, Sam wasn’t sure he’d ever known immediately what desire felt like until he first really looked at a priest.
He fondles Dean’s collar as he bounces in his lap, calls him Father with each breath, and gets praised for taking his penance in stride.