Sam was getting real damn tired of Dean's weird behavior. The older Winchester was texting - texting - and giggling. Honest-to-God-I'm-sharing-a-motel-room-with-a-teenage-girl giggling.
Maybe Bobby finally figured out how to text and they were joking about something. Yeah, that had to be it, right? Because the only other person Dean knew besides Sam and Bobby was Cas, and he barely knew how to make a call, there's no way he knew how to text.
But the Bobby explanation didn't cover Dean receiving a text, leaping from his bed, running to the bathroom, and returning less than a minute later with a smirk on his face.
Sam couldn't take it anymore. "What the hell are you doing?" he snapped.
Dean looked up at him, already sprawled back on his bed. "Sexting," he said with another smirk and a tell-tale waggle of his eyebrows.
"With who?" he asked, incredulous.
"Cas," Dean said, smirk turning into a gleeful little smile.
"Cas," Sam repeated, doubt shading the word. "You're sexting with an angel of the Lord? Do I want to know how you managed to get him to do this? And why are you giggling if you're sexting?
"What can I say, the dude's into me. And I'm not giggling, Sam, it's laughter. Manly laughter. And I'm laughing because he's not very good at it."
"I wouldn't expect him to be, Dean. What was with the mad dash to the bathroom?"
Dean grinned, clearly satisfied with himself. "I went in there to take a picture of my dick. Figured you'd get mad if I just whipped it out right here. Plus, y'know, didn't want to overwhelm your eyes with the impressive-"
"Yeah, I get it," Sam said, holding a hand up to stop the onslaught of terrifying imagery now in his head. "Thanks for the consideration, I guess," he added, but his words fell on deaf ears because Dean was giggling again, and it was indeed a giggle, at Cas's newest attempt at sexting.