A zipper

Before his rational mind could come back, Sam's fingers grabbed his zipper and pulled it down. His cock sprung out. It was thick, hard, and the head was glistening with precum.

Jasmine should have panicked, should have screamed, should have looked away. But all she did was whisper, "Wow..."

She had no idea how big her big brother really was. Nearly twice the size of her boyfriend, and it looked much thicker. And somehow, her raging libido told her that it was all hers.

Sam didn't stop to let his conscience talk himself out of this. He needed this. His fingers grabbed hold of the base of his hard cock, and his hand started stroking up and down slowly. As he started to rub himself, Sam's eyes were glued on Jasmine's body. Her cute, blushing face. Her hard nipples poking through her top. Her thighs rubbing together, almost in time with his hand. Her own hand... disappearing in the waistband of her shorts.

Jasmine didn't have time to think about what she was doing. She needed this. Her fingers glided over her soaked pussy, grinding slowly. Her finger tips found her swollen clit, and she let out an involuntary noise that her brother was never supposed to have heard. But she didn't care right now. Her finger grind faster on her clit as she leaned back against the wall of the elevator.

Both of them were picking up pace, masturbating together in the elevator while watching each other. Neither of them dared to speak, for fear of breaking this spell of lust that's covered both of them. Jasmine's shorts were slipping down, revealing to her brother that she wasn't wearing any panties. Sam shifted to face more towards his sister, both to get a better look at her and also to enjoy this show. Their eyes met, and they didn't even slow down. They both silently knew where this would go.