She's mad

You're having a wonderful erotic dream about Amy and her sister when you are awoken by a soft yet firm object hitting you in the face. Your eyes open and you see Trish standing by the bed with a pillow in her hand. You notice that she isn't wearing a bra under her t-shirt.

She hits you again and says, "Jerk! All the girls here at this school and you sleep with my little sister!?”

“I'm sorry,” you say sheepishly.

“And you ...” Trish says as she spanks her still sleeping sister's bare ass with the pillow. You find this arousing. You know Trish didn't intend it as a sexual action, but your rapidly hardening cock doesn't know or care.

Amy opens her eyes and smiling up at her older sister says, “Hi, sis.” Then Amy rolls onto her back and you can't resist staring at her beautiful bare breasts and pussy. Trish notices and hits you in the abs with the pillow.

“Put some clothes on, Amy!” she demands.

“Why?” Amy asks and glancing sidelong at you she adds, “it's not like he hasn't already seen me naked”.

“What does that mean?” Trish asks.