The covers were drawn up to her shoulders as she was on her side facing away from me. I looked down towards the bottom of the bed and saw the black sa...in corset she had been wearing thrown on top of the covers. She must have awoken in the night and found it uncomfortable to sleep in and taken it off.I slid quietly over next to her and buried my nose in her lustrous brown hair. I breathed deep and her young girlish scent filled my nostrils. She smelled of shampoo, a young girl’s perfume, sweat. They were all looking forward to some pizza but were also starting to think about other things that a woman’s mouth might like to have in it.Once again the cheeky Philippa Boyd spoke up.“I have a dare!” Everyone went silent. “I want Janet and Becky to order and collect the pizzas in the nude. They are Absolutes so that won’t be a problem for them but I dare Danny and Peter here to stay nude while we walk across the Campus and over to Becky and Peter’s Bungalow for the evening. They have to stay. Her ass convulsed around my cock, and she screamed into the ottoman, and I paused horified, realizing what I had done, what I was doing.After a moment of just standing there my cock halfway in my sister's ass I felt her move, I couldn't believe it as I realized she was pushing back into me."Cum'mon, brother, fuck your little sister's tight ass. Shove that big fucking pole in there."I almost blew my load right then and I groaned with the encouragement. I began rocking back and forth getting my. When I was finished with the problems, she checked them and congratulated me on solving them all correctly. She then presented me with a second sheet, with eight or ten new problems. Then she excused herself and left the room. I presumed that she was going to the bathroom. As I was finishing the last problem, Ms Paddyspurs reentered the room; she had taken off her black dress and now was wearing a black lacy full slip. Taking the paper, she checked my answers and again congratulated me on.