This story was originally meant to be a one-shot, I have since decided to split it into three parts. I am not sure where this fic takes place, I would say Season 3 somewhere. Allison and Scott are broken up and this story would fall somewhere before Kira and Malia enter the picture. I love the idea of a Stiles/Derek relationship and wanted to make this as authentic as possible. Hopefully I did the characters justice.
Song paired to this ficlet: Apathy by Mr. FijiWiji

Derek was not impressed. Crossing his arms he narrowed his eyes moodily at the crowd of salivating women before him. They weren't even trying to form lines, simply toppling over each other in an attempt to be first.

"Stiles I am going to kill you" he gritted out bitterly to the boy sitting next to him.

"Yea I'm okay with that" Stiles breathed back eyeing up the women excitedly, teenage eyes wide and hopeful.

Derek grunted in frustration tugging at the ridiculous red hat on his head. The material was making his head itch. It had been Stiles' idea of course. Stiles had all the bright ideas didn't he?

When Scott had approached Derek earlier that week and had started his sentence with "Dude, Stiles has a great idea" Derek should have known. When did Stiles Stilinski ever have a great idea? Instead of ending the conversation immediately Derek had ever so slightly tipped his head down, an invitation to keep talking.

Now look where that had gotten him. Sitting in the middle of the mall with a Santa hat on his head and a sign hanging above reading Kissing Booth all proceeds go to Charity. Scott and Stiles sat on either side of him looking as stupid as he felt in their matching Santa hats. Twenty-five cents a kiss hadn't seemed like a lot of money to Derek in the beginning but with the amount of women they had lined up here...Well it appeared they'd be making plenty to donate to the Christmas Dinner Beacon Hills was holding for the homeless. Derek had to admit it was a good cause, he wouldn't be here if it wasn't, but he had a feeling his teenage company was interested in the kissing booth for entirely different reasons.

A lanky arm hit him in the face just then as Stiles stood in a rush, body flailing in its usual awkward display. Derek just glared up at him silently, letting his eyes do the talking.

"Oh-kay" Stiles said slowly giving a lopsided smile and holding out his hands defensively. "Great, you just keep that up, the women will love it"

Derek just kept letting his eyes speak for him.

"Yup...everyone likes the strong, silent type." Stiles muttered before looking away to address the frenzied females before them.

"This is great...so great. Hey I'm Stiles"

The women's chatter died down as they eyed him sceptically.

Beside Derek, Scott snorted.

Oblivious as always when it came to women, Stiles just barrelled ahead.

"I can see you're all eager to get your kiss on...well for charity...not to just kiss us... I mean if you want to kiss us that's a bonus... "

Derek raised an eyebrow in amusement and Scott stood to save his friend from further embarrassment.

"If you would all please pick a line we can get started. Twenty-five cents a kiss, of course you can donate more if-"

The women had began moving frantically to form three lines before the alpha had got a chance to finish his sentence.

Derek eyed the women moodily. He was unsurprised by the results but no less agitated. Stiles had two girls in his line, Scott had about 15 and Derek had about twice as many.

It was going to be a long afternoon.

.

Scott sighed happily putting all his coins back in the jar after counting them. He'd made $50 this afternoon he's said, although Derek suspected the smug grin had something to do with the last girl to visit Scott's booth. There had been some tongue involved in that one. Derek grimaced at the memory of slurping sounds the pair had noisily made next to him. The eldest werewolf glanced down at his own donations. He had no idea what he'd made but he'd filled 2 jars so he figured he'd done well. His eyes slid over to Stiles' nearly empty jar.

If the younger boy was upset by the lack of women coming to his line for their twenty-five cent kiss he hadn't shown it. He had been eager with all six of the women that had lined up that day bouncing happily on the balls of his feet each time he leaned over to place a chaste kiss on the lips of the donor. Even now he was grinning from ear to ear while he picked up his jar.

Derek stared pointedly down at the near empty jar but Stiles' smile never wavered.

"Women find me intimidating" was all he said with a shrug.

Derek hid his smirk by turning away to leave.

"Same time tomorrow?" Stiles called out after him.

"Tomorrow." Derek replied without turning around.

.

Derek returned to the mall the next day as promised. Stiles and Scott were already at their booth jars out before them and a small crowd of ladies in line for their kiss. Sending a wary look in the women's direction he took his spot among the teens and placed his jar out in front of him.

"You're late" Stiles murmured from beside him.

Derek ignored him. Let day two begin.

.

Given the previous days lack of excitement Derek had been expecting much of the same the second time around. He was, however, severely disappointed. It began with the tall blonde who'd found their way into Stiles' line. Tall, Blonde and as fate would have it, male. The man happened to be exactly two women away from receiving a kiss from the one and only Stiles Stilinski. Derek caught the nervous look Scott and Stiles shared from either side of him. Stiles couldn't, of course, refuse to give a kiss just because the recipient was a man, their booth certainly didn't say no men allowed. Derek for one would enjoy seeing Stiles squirm, served him right for using a fundraiser as a way to pick up chicks.

Derek tried to focus on his own line of women but try as he may he couldn't stop his eyes from sliding to the left where Stiles was finished giving the last girl ahead of the blonde man his signature quick peck. He could smell the anxiety coming off Stiles in waves, heard the nervous gulp, saw the clenched fists. Seeing Stiles this way was starting to make Derek himself increasingly uncomfortable, the smell of him alone was enough to make Derek's stomach toss and for reasons he didn't entirely understand he was standing and locking eyes with the blonde stranger. Steel grey eyes met his unflinchingly and Derek got the impression he was being challenged...challenged for what, he didn't know.

"We're going to be taking a break now" was all he said not breaking his stare with the other man.

Perfectly shaped blonde brows narrowed angrily and Derek was no longer just getting the impression he was being challenged, he knew he was.

"Is that so?" The grey eyed stranger broke eye contact with Derek and was looking at Stiles now. The women, still in lines at the booth stared on anxiously, quiet for once, along with Scott.

"You mean the break? I mean that depends on what you consider a break, like are we talking like sitting here or maybe like leaving the building because-" Stiles rambling ended abruptly as the blonde leaned across the table his mouth firmly meeting the shorter man's still moving one. This kiss was not like the many others Derek had witnessed Stiles receive in the last twenty-four hours. It wasn't shy. It wasn't innocent. It was wanton. It was...aggressive. The blondes hands rose to cup Stiles jaw, thumbs caressing the skin there and Derek watched as a tongue was slipped into Stiles mouth. Derek listened as Stiles heartbeat picked up speed, heard the whimper of pleasure that escaped Stiles mouth. An unfamiliar scent wafted through the air, sweet and musky all at once. Intoxicating. It took Derek a moment to find the source. It was Stiles. More accurately, Stiles' arousal. Before he could stop himself, before he even had time to think about what it meant or the consequences of it a deep and low growl ripped from his throat. Something was thundering, roaring... somewhere in the back of his enraged mind he recognized it as his own heartbeat.

"Derek" Scott warned placing a hand on his shoulder. The older werewolf shrugged his hand off eyes still locked on Stiles.

He'd broke away from the kiss, lips swollen, eyes wide, staring at Derek.

"Dude," Stiles took a step away from the man and towards Derek slowly "Your eyes."

Scott's hand had found it's way back to his shoulder squeezing gently and turned Derek to face him. "Calm down, man, just breathe."

Derek took a sharp intake of breath through his nose, exhaling it slowly through his mouth and feeling his eyes shift back to normal. He glanced up at Scott, his eyes clear, and the younger male nodded his head before allowing his hand to drop from Derek's shoulder and turning away to speak to the confused bystanders.

Derek found he couldn't focus on anything but Stiles. He had his hand out before him cautiously looking torn between approaching Derek and running away.

"You okay, man?" Stiles asked hesitantly.

Ignoring him Derek spared a glance at the blonde who was still standing there quietly, a satisfied smirk on his face.

"That'll be twenty-five cents" he snapped waspishly.

The blonde man eyed Stiles with an unmistakable look of appreciation.

"My pleasure."

We are just going to assume that the only people that seen Derek's eyes change are Scott and Stiles, just in case there was any confusion.
Also wanted to do a quick shout out to NinaLima22 on youtube. It was her Sterek video, Apathy, that became my muse and inspired me to start writing about this pairing. If you haven't seen the video please do yourself a favour and check it out, will post the link below.
watch?v=-v7YuXCKXM