He thinks about in the shower but doesn't really know where it comes from. It's been a long day at work, the winter has arrived and the heating system is broken at the bookshop where he works. He's been cold all day. On his way home the only thing he could think about was the warm shower he'd take and how he would cuddle the hell out of Stiles when he would be back home too.
There wasn't a lot of customers today so he got even colder by sitting still. He can't blame people for not wanting to come in the cold shop though. He read an interesting new book they have, it's about identity. Two things stayed in his mind. First, the fact that your face is one of the things that makes you so unique and yourself but you never get to see it directly like people looking at you do, like you see your hands. And there was this thing about names. He didn't actually finished the book because it reminded him a little bit too much of one of his psycho exes. But thinking back on it he thought about Stiles who's name is only something he picked because he didn't like his real name, people not knowing how to read it, or pronounce it. People often make a weird face, even when he tells them to call him Stiles, the reason is probably that they think it's special to name your kid like that. But Stiles likes it.
Derek has read Stiles name many times. He's seen it regularly on envelopes or important papers over the years. He wrote it a couple of times, too. When they moved in together he was the one who wrote both their full names for the mail box and the bell. He never heard Stiles, or anyone, say it though, so he never tried to do it himself, not sure how he could pronounce that.
He never gave it much thought until today. But the thing is, everybody call Stiles by a nick name and, shouldn't a nick name be somewhat personal? Aren't nick names something you give your close friends or family? Your lover? Stiles calls him baby, not all the time but when he doesn't really think or when he wants to be comforting and sweet. Derek? He calls him just the same way than their friends do, and his dad, coworkers and most of the Police Department of Beacon Hills. Except Scott calls Stiles weird things that has a meaning just for the two of them. Lydia calls him sweety half of the time. And let's not talk about the old woman that lives next to the house where Stiles grew up. The Sheriff calls him son, or kiddo (and, well, Derek doesn't really want those for himself).
Derek feels like he's missing on something, not having a special way to call Stiles. He doesn't want to try and fail at calling him by his really real and strange name. The leads him to, still in the shower, think about how to call the man he's been living with for four years.
He thinks about what he knows, or used to. He remembers his mom calling his dad honey, and shakes his head. That won't work. Peter always used weird things to call his wife and Derek doesn't want something girly anyway. He doesn't think about what he's been called by his crazy exes, obviously. That would be incredibly awkward, disgusting actually. He tries really hard but everything seem too much, too cheesy and unnatural. When Stiles calls him baby, it feels like there is no other way he could call him (probably because he always seems to chose the right time to do it). He wants to find something that sounds right. Like he feels right when he's with Stiles. He wants something intimate but not too stupid (even though he's stupidly in love).
When he's done showering and dry, Derek opens his laptop in the living room. He looks around him, like someone could be in here watching what he does (and it's over that time when everyone had a key and let themselves in all the time, it's over since almost everyone managed to walk on Stiles and him having sex, plus Stiles is at work for another two hours), and types in the search bar 'how do I call my boyfriend''.
He closes his eyes and sighs, feeling stupid. He wants to do things well, it's been like that since the beginning. This is not the first time he types something stupid in a search bar to know how to relationship. (There is that epic time when he asked the internet 'how do I tell my boyfriend I want him to fuck me'. Stiles had arrived in Derek's former apartment early, Derek had quickly closed his laptop. He had tried not to blush when Stiles had kissed him and got up from the couch to go make dinner. When he opened his laptop again, a couple hours later, after Stiles had left, his ask bar answered 'LIKE THIS IS OKAY'.)
When Derek opens his eyes and starts clicking the links, all he finds is the same question asked by teen age girls and nothing good comes out of the search. He clears his history (because he really doesn't want Stiles to find this) and moves on. He decides to let it rest a little a bit in a metaphorical box in his head. Maybe he'll come up with something in his sleep or while jogging (his brain does great things when he's running).
Derek realizes the next Sunday that you don't just make up names to call the person you're in love from a list on the internet. It happens. Just like Stiles calling him baby happened.
They're having breakfast in Stiles favorite coffee shop because they were too lazy the day before to go grocery shopping and don't have anything to eat anymore in their kitchen. Stiles is being his stupid self, making the new waitress fall in love with him (and Derek a little bit more), eating like a dog, saying himself how he looks like he was the one raised by wolves. They talk about nothing, really, because it's Sunday morning and they just want to be together peacefully, and simply enjoy each others company. Stiles has eaten two plates of pancakes and his coffee is still to warm for him. Knowing that they wont eat lunch any time soon, Derek asks, “Do you want a Stiles, muffin?” He frowns, repeats what he just said in his head because it didn't sound like it should.
Stiles laughs and before Derek can correct himself says, “Sure, bring the Stiles! But you eat it out.” Derek's eyes widen at the blatant innuendo. He blushes at Stiles' lustful smile.
Stiles laughs again since embarrassing Derek in public places is one of his favorite things to do and says, “the raspberry one, please?”
Stiles gets his muffin and once they're back at their place he takes his clothes off in the living room and shoves away everything that was on the coffee table. Then he lays on it, on his back, heels at the edge and legs spread wide. “Now come here and eat me like one of your muffins.”
If Derek wasn't already all hot and bothered seeing Stiles like this, he probably would have facepalmed.
Later, when they're snuggling in their bed, the sun warming the room and reflecting in Stiles eyes just the way Derek likes, Stiles says, “it was cute actually.” Derek raises an eyebrow, not understanding what he's referring to. “You basically called me muffin. That's cute, cause muffins are really cool.”
“I loved the peanut butter and chocolate ones my mom used to do.”
“I'm sure we could find some recipe somewhere and try to make some,” Stiles says softly. Derek smiles and buries his nose in Stiles' fluffy hair. He likes it when Stiles brings back good things from his childhood, good memories they can share instead of being held back by bad ones.
He mumbles “muffin,” against Stiles warm skin and knows that he just found the perfect way to call him. It is cheesy, yes, but so is baby. The point is, he didn't pick the name from a list. It will just be the reminder of one of those perfect days when there is nothing but the two of them that matters.
And Derek always ate his mother's muffins still a bit warm, liked them better that way. It fits with Stiles eyes and how warm his love makes Derek feel.