Ok, so this is kind of inspired by this:
Or more acurately, why I disagreed with their characterisation. Actually the end product is more similar than I intended but I still don't think Cas would be so understanding. And I really don't think Dean would care.
"Cas, I really don't see what the problem is."
Castiel gave Dean an expression that looked like it could sink ships and, in fact, actually had. Loud and expressionless, Castiel yelled. "Stiles has mated, Dean."
Dean rolled his eyes. "You really have to stop calling it that."
"Biologically that is its function."
"Cas, that would only apply if one of them was a woman. And I'm fairly certain Stiles is gay."
Cas shrugged in a surprisingly human manner. "Stile's sexuality has never been solid."
Dean eyed him off. "It hasn't?"
"Not since he was a baby." Cas stated this as if it were the most obvious thing in the world.
Dean's eyes widened. "Right, because you can speak baby?" Actually that made a lot of sense to him. Cas may have been good at many things, but his baby talk seemed far too low to be normal. Dean had just always assumed angels didn't feel the need to speak high pitched to babies.
"Don't be ridiculous, Dean. I can tell a human's sexual orientation merely by looking at them. All angels can."
Dean gave a little sideways nod. That made even more sense. "Ok, that's great and all, Cas, but why should I be worried. It's not like Stiles can get pregnant."
Cas looked absolutely terrified, as though the thought that Stiles, maybe, could get pregnant had just struck him. "It's not pregnancy that worries me." He said, unconvincingly. No one really knew what nephilimwere capable of. "It's the possibility that Stiles may have caught a STI."
Dean felt like slapping himself in the forehead. "Why do you care? You brought me back from the dead; can't be that hard to just zap him better?"
Cas shook his head a little. "That's not the point, Dean. We need to teach Stiles proper sexual practices. We won't always be around and I am certain Stiles did not use a condom-"
"I'm not even going to ask how you know that."
"And secondly," Cas continued as if Dean hadn't said anything. "Derek is a child of Eve. It is entirely possible he carries diseases that are beyond my powers to heal."
"Why would the Mother of All make diseases that affect her own creatures?"
"Only my father is a worse parent."
Dean gripped his temples. "Fine! Whatever! We can cross that bridge if we get to it. Hell, I've been cured of vampirism, I'm sure we can get rid of a bout of crabs."
Cas looked a little nervous. "I do not know underst-"
"Forget it!" Dean looked Cas dead in the eye and said. "If you want to have this conversation, go right ahead. I won't stop you. But I'm not helping you either."
"But I need someone to change the slides."
Dean groaned and stomped out of the room determined to find the enochian wards he always kept on a necklace. He really didn't need Cas teleporting after him right now.
"Oh my God." Dean heard Stiles shriek from the other room. He couldn't help but snicker at that, he wasn't exactly engrossed in the utterly normal newspaper in his hands. Not a single weird murder or disappearance. Sometimes he hated this domestic thing.
His gaze snapped up as Stiles slammed the door open, his arms flailing wildly around him. For the life of him, Dean would never know where he got that from.
"If you close the door now the wardings will stop him from getting in." Dean growled. He attempted to throw the paper down onto the arms rest, missed, and then pulled himself uncomfortably to his feet.
Stiles slammed the door shut as soon as he heard, the entire house shaking slightly with the effort. "Do you know what he was trying to explain to me?"
"How to use a condom?" Dean asked.
Stiles looked uncomfortably at him for a moment. "Yeah..." His eyes quickly darted away from him. "I was kind of hoping I'd get to yell that at you."
"Did he use a banana?" Dean asked.
"No, in his words, they're not 'anatomically correct'." Stiles said, looking a little green.
Dean grimaced. "Jesus. That's messed up."
The sound of flapping wings could be heard beyond the door and then the knob started to rattle. "Dean, I can't come in when the wardings are up!"
"That's the point, Cas." He yelled back. "Stiles didn't want you to come in."
"But I was trying to help! He doesn't know what he could catch from unprotected sex. Herpes, Hepatitis B, HIV AIDS-" Dean heard Stiles humming something which sounded suspiciously like Lady Gaga. He looked over and saw his fingers jammed in his ears. "Vampirism, Pubic Lice, Suphuluphuclupicus-"
"We get it, Cas, and Stiles does not want to hear about it."
"I haven't even got to-"
"Cas, how about I give him the talk?" Dean interrupted, a little anxiously. Stiles, his fingers still jammed in his ears, turned slowly towards his Dad, suddenly very pale.
There was a moment of silence. "Would you show him how to use protection?"
Dean rolled his eyes. "Yes, Cas, now leave."
"Of course, Dean." He heard the flutter of wings and then silence from beyond the door.
Stiles' normally pale face had turned the same colour as the walls, something which should have beyond human ability to reach. "Please tell me you were just trying to get rid of Pa."
Dean chuckled and slapped his hand on Stiles back, pulling him into a hug. "Stiles, there is no way in hell that I'm giving you the talk."
Stiles let out a sharp breathe and wiped the sweat from his brow. "Well, that's relief. So, if I tell Pa that you discussed it with me, I can go?"
Dean smiled. "On one condition."
Stiles' eyes widened and he loosed a nervous little chuckle. "What is it?"
"You tell Derek this. If he hurts you, I will run him over."
Stiles smiled. "That's surprisingly civil of you"
Dean gave Stiles the biggest and scariest smirk he'd ever seen. "Did you know the Impala has a silver bumper?"
If any of you are following my Avengers story, I AM STILL WRITING IT. I'm sorry about the wait, but I can have two chapters up by tomorrow. I might wait a bit because I want to give you three, and the next one is very long, but oh well. It is coming. And I write this here cause I don't want you to get your hopes up.