Dean should have sensed danger when he came back to their latest dump of a motel room, and Sam smiled at him. That really creepy “I know something you don't know” smile. But Castiel was there for a change, so Dean was a little distracted.
“Hey, Dean. I just found out something interesting,” Sam said, his grin growing steadily more smug.
“Oh, really?” Dean said, trying to look like unpacking the food was a vital task, and whatever Sam was about to say wasn't interesting in the least.
“You know how you always call the angels 'junkless'?”
Dean snorted. “Yeah?”
“Well, as it turns out, you were closer than you think in at least one case.”
Dean turned around to face Sam, just in time to see Castiel turn his eyes heavenward next to him.
“What are you talking about?”
Castiel frowned at Sam, but this only made Sam's grin turn positively gleeful. “Cas is a girl!”
Dean cast a glance at Castiel, who tried to look indifferent, but kinda failed.
“I'm pretty sure I would have noticed that,” Dean ventured carefully, trying not to think of all the times Castiel had popped in on him in bathrooms and bedrooms.
“Sam, please,” Castiel interjected. “I told you, it's not that simple.”
“What?” This Dean had to hear.
Castiel did his half eye-roll again and cleared his throat. “Sam asked some questions about vessels while you were out, and I explained as well as I could.”
“Like how you can be in vessels of any sex,” Sam grinned.
“I thought you guys didn't have any genders?”
“We do. However, they translate very poorly to the human concepts of sex and gender identity,” Castiel explained, as if he was already really tired of this conversation.
“But Sam says that you're...” Dean picked his brain for something that sounded a little less pre-school. “...of the female persuasion.” Smooth, Winchester.
“And like I said, it's not that simple. Angel genders are plentiful and endlessly fluctuating. But if pressed, I would have to say that certain aspects of my being indicates that I would fall closer to female on your narrow spectrum of gender.”
Dean blinked. “So...”
“So!” Sam cut in, smirking. “That means he's more girl than guy!”
“In the broadest possible sense.”
“Well... uhm. That's cool. I guess. No more popping up in the bathroom, then, please.” Then something else occurred to Dean. “Does this mean I have to call you 'she'?”
Castiel looked like he only narrowly avoided rolling his eyes. “There's no need. I'm currently in a male vessel, and there would be no point in making things more complicated.”
And that was supposed to have been it. Dean knew this. But that little voice in the back of his head, the one that sounded an awful lot like his dad sometimes, kept heaving little sighs of relief. It was as if the idea of Castiel not being 100% guy made it somehow less wrong to have those... thoughts... that he sometimes had about the angel. Which was kinda the tipping point. Angel. Guy or girl, it really shouldn't matter. It was still kinda wrong.
But the voice in his head whispered “Anna” and no matter how many times Dean tried to tell the damn voice that Anna had been human at the time, it still ended up exactly the same place every time. He'd banged an angel. And goddammit if he wasn't jonesin' to try it again.
Yet, that wasn't actually the worst part. As much as he tried, he just could not help acting differently around Castiel. He could see it happening, even as he tried his hardest to prevent it. But it was like watching a train crash in slow motion. Horrifying and predictable, yet completely unavoidable.
And Castiel noticed. Of course he did. He noticed if Dean had a paper cut, for fuck's sake. Of course he noticed when Dean started stepping aside for him in doorways, and smiling at him instead of saying a filthy joke. Dean was well aware how fucked up he was once he actually started flirting with Castiel. Sam, predictably, thought the whole thing was hilarious, but at least Dean had a lifetime's worth of training in ignoring pestering younger siblings.
Ignoring Cas, on the other hand... where it had been difficult before, it was now utterly impossible. Everything he did was now run through Dean's brain and put on the scales of “girly or not”, as if it were some bizarre quiz show. And while the scales did tip pretty heavily to the “not-girly” side, it was still as if every hint that there might be some form of female inside the ad-space salesman made Dean's douchebag behavior somehow valid. Logically, he knew he was being an ass. But as always in company just vaguely female, annoyingly, Dean's dick tended to take over thinking now and again. Which was very, very bad.
Clearly, even Castiel had his limit, because one night, after one more ill-timed wink-and-smile that Dean seemed stupidly incapable of keeping in these days, Castiel squinted at him before dragging him outside by an iron grip on his shoulder.
“Ow! Jeez, Cas, what!?”
“You've been acting differently around me, Dean. I don't know why, but I would much prefer it if you would stop.”
Dean tried to think of some kind of defense to that, but in the end he just let his shoulders droop and groaned. “I know, and I'm sorry, Cas. I just don't deal with this whole gender thing all that well.”
“Because I'm a douchebag, apparently.”
“I don't agree. But why would this issue make you a... douchebag?”
Dammit, Dean would give anything to not have to have this conversation. Because as much as he wanted to, he had real trouble lying to Castiel's face.
“It's... complicated,” he hedged.
“But it's posing a problem in our interactions. So please try and explain it to me.”
“Look,” he started, drawing a hand roughly across his face in frustration. “I'm different around girls, okay? It's like... as soon as there's even a remote chance of getting laid, my damn brain goes out the window!”
“I'm not sure I understand. You believe that your chance of having sexual intercourse... with me... is greater because I am... less male than you previously assumed?”
“Ye-no! No... I mean... yes, but... I told you, it's complicated.”
Castiel gave Dean a long piercing look, and he could feel his throat close up just being under that much scrutiny. Eventually Castiel frowned and said flatly: “I see two immediate problems here, and in my opinion they're both easily fixed.”
Dean felt his eyebrows shoot upwards. “Oh? Well do tell, Mr. Wizard!”
“First of all, you have never asked me if I would have sex with you. If you had, I would have accepted.”
Dean swallowed thickly. “O...kay.”
“Secondly, you seem to assume that me being more woman than man would somehow make me physically weaker.” He stepped in close, crowding Dean against the wall of the motel. “You forget all too easily that should I wish to, I could crush you in an instant.” He put his hands on the wall on either side of Dean's head and his jaw dropped open as Castiel leaned in until they were almost nose to nose.
“And while my true form might be closer to female according to your limited concepts of gender, I can assure you that my current vessel is very much male.” Dean would have complained about how Cas basically made humans sound stupid, but when he closed that last bit of space between them, and pressed his very obvious hard-on right into Dean's hip, all Dean could utter was a strangled “guh!”
Castiel leaned even closer, bringing his lips right up against Dean's ear. “If I show you just how male I can be... will you stop treating me differently?”
Dean shivered. “Uh... I dunno. Guess we'll have to try it and find out.”
Castiel made a purring noise, and Dean would claim to the end of his days that he totally did not whimper at that. Only, he totally did.