It was a complete surprise, though it shouldn't have been, when John picked up the Ancient Device and Something Bad Happened.
Rodney had found it in an abandoned part of the city, on what seemed to be a bookshelf, the Ancient writing on it a spiderweb, as dusty as things got in Atlantis. It was black, a pure black, light-absorbing.
John said it looked like the spaceship in Hitchhikers' Guide to the Galaxy, the one that was so sleek and black, it didn't exist. Rodney dismissed that idea with a wave of his hand.
So John had picked it up to run his hand over it, and, surprise, it glowed pure white.
And suddenly there were two Johns.
John The Original (at least Rodney thought he was) was silent for a couple seconds, staring at his clone (Twin?), while John the Fake grinned rakishly and took off.
"Crap. I can barely handle one of you, you know," Rodney slumped in his desk chair.
So of course Rodney should have realized what was happening when John cornered him in a transporter late that night on his way back from the lab.
"God, Rodney, handle me," and suddenly the transporter was too small, too cramped, and Rodney was between John and the wall and Getting Claustrophobic. He panicked for a few seconds before John's mouth was on his, and then his brain melted out of his ears.
It took Rodney all of five seconds before the shock wore off and he got with the program. Groping, fingers against flesh. Tongues slid against lips and teeth and cheeks, left trails like snails across collarbones, and all the while there was nothing but wet silence and rustling.
"John...?" It was more of a sigh of relief than a question, but John answered it anyway in the pressing of his body, the jerking of his hips. That was animal desire that rocketed through them both, basic, instinctual. So Rodney, by instinct, pushed John's pants down to his thighs and arched his back.
John made a kinky noise, keened as he ground his hips and did the same to Rodney's pants, and then it was just them, exposed, intimate. John grabbed Rodney's wrists and pinned them with one hand above his head to the wall of the transporter, kept Rodney from completely letting go, so they slid skin against skin in random thrusts, building momentum as John's free hand explored hair and chest and backside. Rodney squeezed his eyes tight shut and bit hard on John's lip and the world exploded behind his eyelids like an Atom bomb, and he felt John, hot and sweaty and solid before him shudder and rumble like a volcano.
A minute passed and Rodney realized they were on the floor of the transporter, entwined like vines and cramped, and Rodney had a Helena moment, a second when all the pieces fit together (Demetrius has not come to his senses, it is all a malicious trick, right?).
"Stupid, stupid, stupid," he chanted to himself, suddenly and irrevocably angry at John for picking up that device. Meanwhile, Other!John (he had recognized this familiar stranger finally), was cleaning up Rodney's stomach with a warm mouth, pink as grapefruit and just as forbidden, and he shoved him away.
"Rodney?" John's voice was hesitant, so him that Rodney almost faltered, but he knew better.
"Just go," he moaned miserably, and without looking up, knew John was gathering his uniform and punching a button on the console. He heard the doors open and waited to hear John's footsteps. Instead he felt a ghost of fingertips tracing the edge of his lips, and then John was gone and Rodney was alone with his misery and self-hatred.
Rodney knew he would sort the whole thing out later, figure out at the eleventh hour how to reunite the two halves of John (of his best friend, of his best male, strictly platonic friend), and John would have no memory of his other half's activities. No memory of his best friend's teeth on his lip or his fingertips bruising hipbones. It will be worse than a half-remembered drunken night because to John, it will have never happened at all.
But Rodney would be forced to live with it, to struggle with the fervent wish that the stranger in the transporter was exactly who he wanted it to be, and not a copy or a clone, least of all a mistake.
And then they fix the problem and John is whole again, Rodney is congratulated, and things go back to normal for a few days.
Until John comes to Rodney's room late one night, forces himself in and shoves Rodney against the wall.
"Hey! Watch it!" Rodney rubs his back tenderly and then John is in his face, almost too close, robbing Rodney's breath.
"Did you think I wouldn't remember? Huh? You think it'd just go away like all your little problems?" Rodney freezes, flashes back to skin and stubble and friction, and he shrinks back into the wall.
"I didn't think you would!" He looks away, but John is everywhere, his presence so angry it diffuses throughout the entire room and Rodney can't escape it, can't escape him.
John slams his hand on the wall next to Rodney's head.
"So you thought you'd take advantage of me when I was literally not myself? You thought you'd work out some of your little tensions while it was convenient for you?"
"What?! No, John, I-"
"Save the speech, Rodney. We're through." John walks out. Rodney is a little limp against the wall before he runs out after him. John is just getting in a transporter, the doors are sliding shut, but Rodney squeezes in and then there he is, inches from a steaming John Sheppard.
"What do you want?" John's entire posture is guarded, defensive yet aggressive, threatening.
"I-" John glares at him and Rodney sees that he can't do it. He can't lose John over something so petty. So he gives in to instinct again and seizes John's vest, pushes him against the wall, and slams his mouth onto his.
John is like steel before he melts, pulling McKay to him, opening his legs, and then Rodney is amazed at his own genius, again, because this is the best idea he's ever had, and John's hands are suddenly everywhere, demanding explanations that Rodney greedily supplies.
They pull apart for air at last, and Rodney manages to explain.
"I thought it was you, you, not other you. I didn't realize till after, I'm sorry-" And John kisses him sweetly, gently. There is promise and forgiveness in that kiss. Suddenly it is all okay.
"You should know," John breathes into Rodney's hair, "That you did handle me very well."