Jack off.

John couldn't help the feelings of lust that were rising in his body, along with his cock, as he watched his little sister, Stephanie, showering. She was lathering her body with soap now, rubbing the suds over her arms; her small, pert breasts; her flat stomach; her beautiful, firm thighs; her killer little ass.

He parted his towel, setting his hardening cock free and slowly stroked it. He pretended that he was in the shower with her, rubbing Stephanie's tits, ass, and suculent virgin pussy. He wanted to have his cock inside her, in all of her holes.