Dean is no way even hoping for a full shower - there's no way. But flinging himself into the bathroom is a distinct possibility if he's fast enough. That doesn't mean he doesn't shoot Lucifer a look of near abject misery for stuffing him into a situation where Sam could easily stumble upon his humiliation. Figures, really.

Watching him dress within the span of a second, Dean is already tinged with adrenaline, waiting for Lucifer to go and make the cuffs to disappear with him. Which just means the second they're actually gone, Dean shoves off the floor like a sprinter, making a mad dash to the bathroom and slamming the door behind him.