A/N Happy Christmas, everyone!

So, I've had a chapter almost finished for a while now, and at first I thought I'd work to get it finished for Christmas, but it's all angst and stream of consciousness style, and I thought, you know what? It's Christmas. I want some good old-fashioned fluff.

So, here you go. This story can be considered canon compliant as of season 8.

Hope you enjoy :)

The Non-Optional Social Convention

Christmas comes but once a year.

Or rather Saturnalia does. Penny rolled her eyes as her gaze fell on the Isaac Newton ornament currently adorning the top of the Christmas tree in 4A. But she refrained from bitching about it.

Not that there was anyone around to bitch to – Leonard had gone out for some oh-so-seasonal Thai food and Sheldon had gone to see Amy at her request – but even still, if someone had been here, she'd have kept her irritation to herself.

Admittedly, being jumped up on homemade eggnog helped with this decision, but it wasn't just that.

Though he didn't say it as much (only freaked out over her hair every few hours instead of every five minutes), she knew the last few months had been hard on Sheldon. A lot of changes in a short space of time; even for someone who wasn't a total whack-a-doodle. Like her and Leonard getting engaged, his giving up on string theory or the constant subtle pressure from Amy to give more.

So if it made him happy to have a weird chopped-off head instead of an angel on top of the tree, or to wear something called a Phrygian cap instead of a Santa hat, then she was happy to go along with it. (It still looked like an elf's hat to her, no matter what he said; though she wouldn't make the mistake of calling it that, or him cute, again – not after the half-hour lecture she got in return.)

So, yeah. She was taking it easy on him. 'Tis the season... or something? The season of keeping Dr. Whack-a-Doodle happy.

Yeah! Good will to all Sheldons!

(She probably shouldn't have had that fourth eggnog.)

Besides, Saturnalia had its good points: Sheldon had somehow gotten hold of a load of greenery and made the most beautiful garlands (where the hell had he found proper holly and mistletoe in California?). That was one of the best/worst things about Sheldon: he was almost as good as he thought he was. Whether it was making zucchini cake, manufacturing Penny blossoms or producing traditional Christmas decorations.

Her gaze fell on the Newton ornament again and she was hit by a sudden craving for cookies. That was the other annoying thing about Sheldon: a lot of what he told her had a habit of sticking in her head, even if it wasn't in the way he expected. Like the fact Fig Newtons were named for a town in Massachusetts instead of the physicist.

Either way, Thai food or no Thai food, she was now jonesing for sweets, so she got up from the couch to raid Sheldon's Satunalia cookie collection.

She was thwarted in her mission by the man himself opening the apartment door. She spun round with a guilty expression and stepped away from the jar. Sheldon eyed her suspiciously for a moment (like he said, he'd gotten better at reading visual cues – at least, better at reading Penny's, though no matter what he said she had not been turned on that day in her apartment), but to her relief he still wasn't quite up-to-speed enough to work out what she'd been about to do.

Or maybe it was just that he had something else on his mind. She noted the slight furrow between his brows and found herself automatically trying to distract him from whatever was weighing on his thoughts.

"What up, Moonpie?"

The furrow deepened. "Nobody calls me Moonpie except Meemaw!" he said reflexively. Then he blinked. "You haven't called me that in a while."

Penny faltered for a moment. It was true, she hadn't. The closer he and Amy had gotten, the more she'd felt she needed to step off a bit. Especially after Leonard had told her Amy was actually a little threatened by their friendship. So all the little quirks they had, the pet names, the special song, the rituals, she'd allowed them to fall away. Made sure Amy knew to do them instead.

Up to this point, she hadn't thought he'd even noticed.

Time to change the subject. "How was dinner with Amy?" she asked brightly.

Sheldon shrugged, removing his messenger bag as he walked further into the room. "Well, the conversation was stimulating as always, but I find myself a weary traveller this post-Saturnalia eve."

She widened her eyes at him. "Why? D'you have to walk all the way back?" (Teasing Sheldon was like that first spoon of Häagen-Daz, near impossible to stop once you'd started.) She took a seat at the kitchen island and batted her eyes at him.

He harrumphed impatiently. "Must you be so literal? There is no poetry in your soul, Penny." He gazed off to one side, looking pensive. "Though I suppose you cannot help that, with your country bumpkin upbringing."

Penny's eyes narrowed of their own accord; good intentions or no intentions, no one could push her buttons like Sheldon. With an effort, she curbed the impulse to take him down, and he carried on talking, oblivious.

"No, Penny. I was speaking of a weariness of spirit."

She felt a slight stab of concern again. He looked... Well, she wasn't sure exactly what he looked, but it wasn't something good. Not unhappy exactly, just not as happy as she'd want him to be. Her head tilted; her tone softened. "Why? What's the matter?"

Sheldon's brow was furrowed again. He clasped his hands behind his back and walked the remaining distance between then until he was standing next to her stool. "As you know I am committed to my relationship with Amy Farrah Fowler, as codified by our legally binding agreement, but with each day that goes by I find the number of actions expected of me as a 'boyfriend'," his tone made quotation marks around the word, "to exponentially increase." His voice began to rise, growing higher with his increasing sense of ill-usage. "As has the number of items considered to be non-optional social conventions!"

Penny bit her lip, feeling another stab. This time from guilt. She was the one who'd told Amy about that neat loophole Howard had taught her all those years ago, when he had told her Sheldon came with a manual. It was a manual she'd learnt to read better than Howard, or Raj, or even Leonard. A manual she'd felt she had to share with his girlfriend.

For the first time she wondered if that was unfair of her. She was friends with Amy, but she'd been friends with Moonpie first. And maybe Amy wasn't so good at knowing when to push and when to back off with Sheldon... The expression "come on too strong" wasn't really one Amy was familiar with... Or maybe was too familiar with.

She paused, the question hovering on her tongue – what had Amy been asking him to do? But she stopped herself. It wasn't her business.

And Amy was her friend, too.

She almost changed her mind when Sheldon's shoulders slumped a little and he sighed. It was only then she realised he'd been watching her hopefully, as if she might have the answers. That was one of their old habits, too.

They were too easy to fall back into.

"Well, sweetie, you know how bad inflation's been the last few years..." She smirked at him.

Sheldon scowled at her. "I didn't even know you knew the word inflation," he said nastily. "Unless it was pertaining to Leonard's gut after partaking of your eggnog."

"Well, I've learnt all sorts of things since I became a pharmaceutical rep," she replied, with false sweetness.

"Like how to score cheap highs outside of vodka?"

Penny winced. That was the downside of the changes between them. They still knew each other back-to-front, but they used that knowledge to make their words wound.

She took another swig of eggnog, wanting to burn the taste of their conversation away. She couldn't really blame him. She'd set the tone.

So she assumed a cheerful one. "Let's not fight, Sheldon. It's Saturnalia, after all."

He wasn't even looking at her. Staring off into the distance again, gaze fixed on a point above her head.

He refocused on her with an almost audible snap, blue eyes skewing her in place. "You're quite right, Penny."

And with hands still clasped round his back, he bent forward and kissed her.

Penny had received more than a few kisses in her life. Sloppy, drunken kisses; heated, skilful kisses; even a few tender, sweet ones. (Two out of three from Leonard.)

Sheldon's kiss lasted no more than a few seconds; it was slightly too firm to be sloppy, slightly too tentative to be skilful, but it was sweet like JD and honey.

And she felt it down to her toes.

It was over before she could begin to compute it, begin to even think of how to respond. Eyelids that had turned heavy fluttered open. Her dazed expression focused, then widened in total shock.

"What the hell was that?"

Sheldon was staring over her head again. His tone was calm, but his cheeks were pink. "My apologies, Penny." He inclined his head to indicate the air above her. "Non-optional social convention."

Penny tilted her head back and finally noticed the mistletoe hanging overhead; she lowered her head in time to watch Sheldon disappear down the corridor towards the bedrooms.

If she hadn't been looking so closely, she might not have noticed the unsteadiness of his tread.

fin