There were a few times that Dean had seen Castiel without his trench coat, and always accompanying the visual of Castiel in nothing but his shirtsleeves and a crooked tie was an overwhelming sensation of "wrongness".
He wasn't entirely sure what it was about the coat, but Dean just knew that Castiel without his trench coat on was like Dean without his beloved Impala; it was just wrong, and Dean knew he'd have to find a way to ensure that the angel never went without his coat in the future.
"You prefer me like this?" Castiel asks him, his brow a quizzical frown as he looks at Dean.
Dean's mouth crooks into a half-smile as he runs his hands down the angel's naked chest- his body divested of all clothing save the trench coat Dean made him put back on.
"Oh yeah," Dean purrs, his body trilling at the feel of the coat brushing against his skin as Castiel moves closer, drawing their bodies ever nearer.
"It… excites you?" Castiel asks, running his hands down Dean's sides- his sleeves rubbing at Dean's skin and eliciting a shiver of delight in response.
"Yeah," Dean breathes, shuffling ever closer, "yeah, it does."
Castiel remembered to always wear his coat from that night onwards.