Becca flipped a braid over her shoulder dismissively.
"What? It's not like you two aren't fucking like rabbits anyway, am I right?"
I looked away. This wasn't the kind of conversation I was going to have with my wife's nineteen-year-old sister.
"Wait, you're not? You're not fucking??" She was up on all fours next to me on the couch cushions.
She put a hand to her forehead and then gestured at me as if to say, But just look at you!
"My sister is suck a fucking idiot!" she said, laughing as she rolled backward, pulling her knees up to her chest.
She was barefoot, in cute gray cotton shorts. I remembered how much I liked her legs. I tried not to look too hard.
She reared up and punched my arm.
"So what? Do you have like blue balls or something?" she asked.
Then she leaned close and lowered her voice.
"Or are you getting your rocks off in other ways?"
I frowned at her. In reply, she just bit her lip and winked.
"I thought so."
She stood up quickly and began to pace in front of me on her tiptoes, scrolling through ideas in her mind.
"So," she said. "I'm just thinking out loud here..."
She turned and faced me, squaring her shoulders. In the shorts and cropped tee, with her hair braided into long brown pigtails that fell down her shoulders, she was the very picture of a bad decision.
"I'm here for the whole holiday break," she said. "Two whole weeks."
She bit her lip again and looked down sheepishly, before she glanced back up.
"What do you say..."
She bent at the waist and put a hand to the side of her mouth, looking conspiratorially toward the backyard where Jenny was taking a work call.
"...I help you with your little—" She glanced down at my crotch. "—'problem'?"
--
All afternoon I thought about it. What I had agreed to, wordlessly, with a single nod, while my eyes had painted my sister-in-law's body with layer on layer of open lust.
In the kitchen as I chopped carrots for dinner, she came up alongside me and traced a hand down over my crotch, whispering in my ear, "I can't wait to get you out of these clothes later."
I twitched against her hand, and she squeezed back.
At the dinner table, with my wife, her parents and Becca all chattering about mundane stuff, I said virtually nothing. How could I possibly focus on anything besides the one thing I could never talk about out loud?
It was a mercifully short dinner as family dinners go, and afterward we circled a fire in the living room, each of us taking turns to go and change into our Christmas pajamas and strut the hallway catwalk to the delighted cheers of the other four family members.
When it was Becca's turn, she ducked out of sight into our spare bedroom for several minutes. I wondered what she'd put on. Should I be afraid?
When she emerged, I sighed with relief. She was covered up, thankfully.
We all cheered, and I blushed slightly, trying to make sure my cheers weren't conspicuously louder than anyone else's.
She wore a full-length thermal onesie in red, with a printed pattern of tiny white snowflakes. Her cute braids emerged from under a Santa cap on top of her head.
But as she spun around dutifully, showing off the whole thing, I noticed an important detail: A cloth flap extended up across her buttocks in the back, two silver snaps the only things separating me from the guiltiest of pleasures.
She looked over her shoulder at me and winked, before dancing across the room and planting herself a little too close to me on the carpet.
When my wife got up to go change into her own PJs and my father-in-law got up to put another log on the fire, Becca leaned close to me and whispered, "Easy access, just for you."
She took the Santa cap off and placed it over my crotch, sliding a hand beneath it and tugging at my clothed cock.
"I hope you're ready for me," she said softly, "because I'm sooo ready for you." Then she licked my ear.
I jumped.
"All right everyone," I said, getting up quickly from the carpet. "I'm going to make some hot chocolate. Who wants some?"
"Ooh, I do!" Becca said. She jumped up. "I'll help."
That was not what I had intended, but there was nothing I could say to stop her.
In the kitchen, she wrapped her arms around me from behind and slid a hand down inside my pants. I felt her slender, cool fingers close around my cock.
"Oh, you're so warm," she said. "And big."
She stepped around me and placed herself between me and the kitchen counter, biting her lip as she grabbed my shirt and pulled me close.
And for the first time, I felt my sister-in-law's lips against mine. She kissed me hard, opening her lips wide. They were soft and warm, and her tongue was inside my mouth before I could protest.
She grabbed my hand roughly and pressed it against one of her breasts.
I groaned into her mouth. Her breast was soft and small, a B-cup like her sister's. It fit perfectly in my hand.
She wrapped a leg around me and pulled my cock against her groin. I ground into her eagerly, holding her and kissing her back.
We stayed like that for what felt like a full minute, warm and entwined, hips bucking against each other, doing what we absolutely should not have been doing.
Finally, she pulled back and looked at me.
"Fuck me," she whispered, with a furtive glance toward the entrance to the kitchen.
"What?" I said. "No, I can't. Jenny's going to be out any second."
"So do it quick," she said.
Without wasting a second, she turned around, pulling open the flap of the pajamas and presenting her naked buttocks, bending over against the counter and raising herself up on her tiptoes.
I was so horny at that point that almost no amount of discretion remained. I tugged at the zipper of my jeans and freed my cock, stepping close and worming it between Becca's legs.
"Mmmm," she moaned. With one hand, she reached back and guided me against her opening, and then I pushed myself into her.
