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You're The Devil in Disguise

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Scott thought when his mother remarried Peter, he’d only see Derek on Christmas break and the odd Thanksgiving. But his step-cousin was always around. Eating Scott’s Oreos and deleting his saved games and shows off the XBOX in favor of his own. Using his hair gel.

Not to mention how his mom dotes on him because Derek does the odd chore around the house. Like cleaning the gutters with Peter is worthy of an extra piece of pie. And he bunks down in Scott’s bedroom some nights, forcing Scott to play host and take the air mattress. It would all be fine if Derek didn’t have that shit-eating smirk on his face when he chased the last of his mom’s infamous cheesecake with his fork at supper or when he’d noogie Scott’s tousle styled hair he spent an hour on in the bathroom. And used his lacrosse equipment. And somehow both simultaneously monopolize the shower and washing machine.

By all accounts, Derek was a butthole. A big one. Scott couldn’t wait for him to graduate and go off to college.

The worst thing was that he couldn’t even complain about it to Stiles. Because Derek was smart. Smart enough to hide the fact that he was douche in front of Stiles. He actually offers to help Stiles with lacrosse, knowing very well that Scott and Stiles always practiced together.

So Scott had to bear with whole afternoons of Derek outrunning him and showing off in front of Stiles.

Derek offers Stiles Scott’s pile of greasy curly fries after tagging along with them to Stiles' favourite greasy spoon dive dinner after lacrosse. Sure Scott would have shared with his best friend, curly fries weren't really his favourite despite coming complimentary with any burger, but there was Derek making Scott look like a greedy friend for not offering. And paying for Stiles at the end of the meal when Stiles had to go to the washroom, footing Scott with his own bill.

Derek even charmingly squeezed in-between him and Stiles on the couch at his house, forcing Scott to be squashed on the arm while Derek whispered snarky comments into Stiles’ ear and basically taking up all the space with his stupid body. Derek’s arm loosely wrapped around Stiles’ shoulders, grinning when they watched Star Wars.

Star Wars and lacrosse was a Scott and Stiles thing. Not a Derek, Stiles and Scott thing. Stiles didn’t even see how evil Derek was.

“I’m on to you,” says Scott with a glare, grabbing the open carton of Hagen-Daas in Derek’s hand, clearly marked with Scott’s name on the side. “Stay away from Stiles.”

Derek merely raises his eyebrows and Melissa and Peter sigh.

“I would think you’d get along, we're family now,” chastises his mom. Scott just backs up glaring at Derek, fumbling for a spoon.

“He knows what he did,” bites out Scott, leaving to eat his ice cream in peace.

It only gets worse when Stiles calls to announce his upcoming date with Derek.