My parents remarried and I suddenly had a new step-sister. She's a student and much younger than me, so I treated her like a kid... It seemed to have stimulated her pride as a woman, and she got angry and said, "Don't make fun of me!" and flipped her skirt up to show me her underwear! She wanted to be recognized as a woman, so she tried to get me to erect, rubbing her ass against me and giving me an assjob, saying, "I'm a body that can do sex properly, too!" If you do that, I'll put it in! We pressed our dicks and pussies together and got so excited that we ended up having sex!