Your sister shows up to the holiday party dresseed, as ususal, like a whore. She loves making fun of you for how hot you think she is. She calls you pathetic for being bothered by her attire, teasing you and showing you her tits all while making fun of you and how much of a perv you are! You can't help it and start touching yourself in front of her and she keeps mocking you while you do for wanting to jack off to her! She even mentons your gf and promises not to tell her since she knows how mad she would be by your sick behavior! In fact your sis thinks the thing that will really make her mad is if she rides your cock! Before you can stop her shes hopped on your cock and is riding you! You never though this would ever happen and when she encourages you to blow your load inside of her, saying it'd be fun to risk it since she won't tell you if shes protected or not, you can't help yourself and you do! Your sis is pissed at you for this saying she was mostly kidding when she told you to cum inside of her! Well fuck!