On their way from the gate room to the locker room, Rodney pulls John into a closet. "Hey," John says, but Rodney's already got him up against the wall and John's pretty smart, he knows where this is heading; Rodney's been hard since John tackled him into the mud to save him from the flying lizard skunks of M47-U55. There'd been a lot of squirming around, the standard threats and complaints, loud predictions of dire alien mud-borne infectious diseases, and then Rodney had frozen, John had made the "is that an Ancient life signs detector in your pocket or are you just happy to see me?" joke, and Rodney grabbed him by the tac vest, yanked him in until they were nose-to-nose, and hissed, "We are so having sex when we get back to Atlantis. I don't care how straight you think you are."
So that's how John knows they're going to have sex, plus Rodney's eyes are looking kind of crazy in an entirely new way and you don't want to argue with him when he looks like that. It's okay. John likes sex. He likes Rodney too, and he'll try anything once.
"Shut up," Rodney says, even though John's not saying a word, and grabs John by the hips and grinds against him like he's got an itch that needs to be scratched. Their pants are slick with mud and they slide together and it's the perfect combination of easy and rough, with their belts and zippers and their cocks rubbing together (two cocks! says John's brain; Rodney McKay's cock!) and it's by far the hottest, dirtiest, weirdest sex he's ever had.
"A little help here, Major," Rodney says. "Put your hands on my ass."
John puts his hands on Rodney's ass, which turns out to be a great idea. Rodney's ass is firm and round and feels fantastic in John's hands, but he's going to keep that to himself, because he's straight, and Rodney's got enough of an ego already. "Sheppard!" Rodney whines, and John gives his ass a good squeeze. Rodney's BDUs are so slippery John really has to dig his fingers in to keep his grip and Rodney groans and his hips jerk forward and he comes in his pants, just like that.
"Cool," John says.
Rodney drops his head to John's shoulder, breathing hard, almost shaking. John pets the back of his muddy neck and decides he's still straight since he didn't come. Except one of Rodney's hands is creeping around between them, kneading John's cock through his pants, massaging the head with his palm; he wiggles his fingers into the front pocket of John's pants, shoves the rest of his wet, muddy hand in there and cups John's dick and it's almost like he's touching John's bare skin; John can feel Rodney's heat, the pads of his fingers (Rodney's fingers! very near your cock! says John's brain) rubbing and pinching and squeezing, like half a handjob, and Rodney growls in his ear, "I'd kiss you if you weren't so damned muddy," and John comes, with his hands on Rodney's ass and Rodney's hand in his pocket and John's brain saying, "Yep, gay now."