Cover up! That's your little sister you perv!
From Create Your Own Story
You quickly take your hand off your cock and throw a blanket over yourself. "Sis! You shouldn't be in my room!"
"What's that in your hand?"
"Nothing! You need to go!"
"Are you hurt, big brother? I'll get mommy."
Oh shit! "No! No, don't do that." Your sister squirms, she isn't used to you yelling at her. "Tell you what, can you keep a secret for me? I'll give you a sucker!"
Her eyes light up, and she nods quickly.
"Okay, I need you to promise me you won't tell anyone what you saw me doing, can you do that?"
"Yeah! I promise! Do I get a sucker now?"