Stepsister's Slumber Party. Mandy has her best friend Valentina over for a slumber party. They're having fun, teaching each other how to twerk & taking videos of one another. Though Mandy is your stepsister and you know you shouldn't be spying on her, you can't help yourself. You love big butts, and both of these girls' booties are so huge.. The girls catch you spying on them and they laugh at you. But they call you over & ask you to judge which of them...