"So, what part of my body do you usually masturbate to? Oh come one! Whenever you are masturbating at home, you are always sneaking looks at me, arent you? its totally obvious.
Didnt you think it was strange?
Im always spreading my thighs out wide in your direction for you to see, conveniently whenever your masturbate, arent I? Im sure you cant help openly masturbating to someone, and Im your sister, so I forgive you. Give me other 50 strokes"