It's in His D-N-A Ch. 01

Wordlessly, he climbed back atop his younger brother.

"Are we doing a rinse and repeat now?" Sam's eyes narrowed in a lewd way.

"Forget about the rinse," Dean said in a low voice. "I always wanted to do a sloppy second after a rough fuck and since you're practically offering ..."

He left the sentence unfinished while taking aim at the cum dripping entrance between the cheeks of Sam's pretty ass.

He made sure that his brother was watching him closely before he pushed his cock through the muscular ring and deeper into Sam's still wet hole.

"Oh fuck!" Dean gasped in excitement as he felt his cock slide through the remains of his own cum. This was so much better than he had ever fantasized ...

"All I need is right here inside me," Sam whispered with a small grin, making Dean freeze abruptly in his motion.

Did he just ... -

"The Antidote? Really, Sam?" Dean let out an involuntary chuckle, barely covering his mouth with his left hand. His eyes were glimmering in both amusement and disbelief. "Out of all the given possibilities you've had there you chose to violate those lyrics?"

"I thought you might like it." Sam's grin widened.

Dean, still chuckling, pulled back until only the tip of his cock was left inside his brother.

"I'm gonna show you want I like," he promised, adjusting his position. Sam blinkingly closed his eyes as Dean slammed his cock back into the tight heat to slowly but surely fuck his younger brother right into delirium.

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To be continued ...

And yes, that's a threat not a promise *smirk+

Anyone wanna count how many times they actually say "fuck"? (spoiler: a lot. that's precisely enough isn't it :D)