Itty-bitty early-seasons McShep, PG-13.
(Mostly an experiment in Rodney's internal voice. This is totally what I think the inside of his head sounds like, at 99 miles an hour, all the time)
Sheppard's lips on his were warm and soft and very, very unexpected. Because of course. Sheppard wouldn't do something like this like a normal person, obviously he would do it in the oddest and most inappropriate manner possible, right in the middle of Rodney's cogent and detailed explanation of Ancient environmental system controls (controls which had to become part of the standard "One hundred and one things to know about Ancient tech so you don't die horribly" lecture for all new Marines, and Sheppard had to approve that curriculum change, infuriatingly, so why the hell wasn't he giving the subject its proper consideration, and why did he think that the proper time for a first kiss was right in the middle of a detailed description of all the ways that improperly set environmental controls could kill a man simply and quietly in his sleep -- carbon monoxide, anoxia, hypothermia -- and really, if Sheppard thought that was a properly mood-setting introduction
Sometime during that train of thought, Sheppard drew his tongue over Rodney's lower lip and coaxed Rodney's mouth open a little.
Rodney pulled backwards (possibly leapt or even jerked a bit, but surprise and the resulting adrenaline do interesting things to muscle control) and opened his mouth for a smooth, suave, cuttingly witty commentary on Sheppard's seduction technique.
What came out was, "You're gay?"
Which, interestingly, hadn't even occurred to him as a fruitful line of questioning during the last .8 seconds of frantic mental wheel-spinning. Because, honestly, "Sheppard is gay" scored somewhere between Boyle's Law and special relativity in the "things that are bogglingly obvious once you discover them" category.
Rodney took a breath to move on to a less idiotic question, and then saw the expression on Sheppard's face.
It was pure unrestrained humiliation.
It only lasted for a split second (long enough for Rodney to mentally compare it to the sympathetic embarrassment on Sheppard's face that one time Rodney walked into the lab to see Miko sobbing on Sheppard's shoulder while he patted her shoulder awkwardly and desperately begged Zelenka with his eyes to do something. This look was significantly less comical and more concealed) before Sheppard smoothed it over. He gave an elaborately careless shrug, said, "It was a joke. Zelenka and I came up with ten ideas for shutting you up. Guess we'll cross that one off the list," and stood up.
"Can you actually think I'm stupid? I mean, after all this time, is that really possible?" Rodney asked. "Because you sound exactly like Faraday when he tried to jump to the top of the fridge and missed."
"Gee," Sheppard said. "Thanks. Put whatever you want in the damn orientation." He turned to the door.
"For God's sake, now you give up? You've never given up on anything in the entire time I've known you, and now you choose to play too-cool-for-school? You're really making me take responsibility for this?" And Rodney reached out to grab him and keep kissing.
("Sheppard is gay" was retrospectively slightly more obvious than Boyle's Law, but the "and you really, really want him" corollary turned out, once discovered, to be slightly more obvious than gravity.)
Happy Valentine's Day, everybody!