For agent1967, because all I could think about as I wrote this was you reading it :) Enjoy!
Dean awoke with a gasp.
He'd just had the most amazing dream. A busty blonde had been topping him, and she'd been so strong and dominating and-
Oh shit. He had a boner.
Rubbing the sleep out of his eyes, Dean trudged over to the shower. He no longer shared a bedroom with his brother, but it still felt way too weird to masturbate in bed.
Dean began to wake up as the hot water poured over his shoulders. He rubbed himself down with soap first, and shampooed his hair, before getting to business with his cock.
A small moan escaped his lips. He hadn't done anything in so long. Tonight was definitely the right time to go to a bar, try hook up with some chick.
What Dean didn't see was the angel staring intently at him moving his hand up and down his dick. Cas carefully watched every movement from Dean's hand, mentally storing it for later.
Dean was jerking faster, imagining the blond that he'd dreamed about. He looked over to the glass, imagining her in front of him-
Dean screamed.
"CAS! WHAT THE FUCK -CAS- WERE-WERE YOU-"
Dean gaped at his friend. His mouth moved up and down, but no words came out.
"What is wrong, Dean?" The angel cocked his head to one side.
Dean spluttered. "You were staring at me in the shower!"
"I fail to see the problem."
"Dude! This- this totally falls under personal space."
"Ah." Cas understood personal space. Clearly he was standing too close to Dean. He didn't quite understand why, considering the wall of glass between them. Perhaps it was to do with the minimum amount of clothing Dean was wearing. Humans were so strange about that.
"No dude- not like that." Dean sighed and rubbed his temple. How the hell was he supposed to explain this?
"You just don't spy on people in the shower, ok? That's just- that's just wrong. What I do in the shower is my own private business."
The angel frowned.
"But Dean, you told me that every human washes themself in the shower, and that every male human pleasures himself once in a while."
"Yes, but-" Dean sighed. How could he possibly try explain this to an angel?
"Just don't spy on people in the shower. That's just- just don't do it."
"But if I can't watch you, than how am I supposed to learn how to masturbate?"
Dean stared at him.
The angel stared back.
"Wait. You spied on me- because you wanted to learn how to do this?"
"Yes Dean, I believe so."
"But how- how did you know I was going to do that this morning? Did you sneak in here every time I went to the shower or something?"
The angel stared at him in surprise.
"Of course not, Dean. That's why I gave you that dream."