With your mother

As evening fell, you didn't see your sister again until your mother came back home from work.

"Hey," she brushed past you before stopping and looking around the living room, "where is your sister?"

"I don't know," you meekly responded, "I think she must be in her room."

Just then, you heard footsteps coming down the stairs and saw your sister, still in her birthday suit, walking up to your mother with an evil grin making contact with your eyes.

"Hey, mom," she chirped. As your mother turned around and saw her daughter in the nude, she gasped.

"Young lady, what is the meaning of this?"

"Ask him," she points at you, "he gets off to women being naked and thinking it's embarrassing."

"Is this true?" your mother starts trailing off and looking down, "is that why you have a stain on your shorts?"

You start mumbling and getting a faster heartbeat as your sister's smile gets wider and wider, and your mother's face grows more and more disgusted.