My step sister Hannah is only 7 months younger than me. Our parents got married when we were 8 and so life since then has been very competitive. We are very close but both very stubborn people and we both hate to lose.

When we were 15 I kissed her best friend Katy and felt her up when she was over at our place to hang out with Hannah. Hannah was super pissed at me. She came in my room the next day yelling 'why don't you get your own friends you're always stealing mine' to which I replied 'why don't you suck my dick Hannah?' And then the fight was on. She said, 'maybe I will, bet you don't have the guts to flop it out' not backing down from the challenge I pulled my shorts off and lay on the bed with my cock out. 'Come get it sis' I said thinking she'd be grossed out and leave but she didn't back down instead she came over 'don't call me sis, we are not related!' She said took my cock in her hand and stated sucking me! We kept insulting each other as she kept giving me head. I had only had one blowjob before and it wasn't to completion. Just a 30sec suck in a game of truth or dare. She said 'I dare you to cum, I bet you won't you're not enough of a man yet' I said 'I will come and you better swallow it bitch' I unloaded in her mouth and she swallowed it all got up and left the room. I'm not sure who won the argument but I'm sure as hell that I came out better off.
Since then whenever we have arguments something sexual happens. A few times we've gone all the way. One time I tried hooking up with her when we were drunk and our parents were away but she wouldn't have it. It's only after a stupid childish fight we both end up so horny and we always abuse each other verbally the whole time. Not sure if we will always do this but it sure is a good way to end a fight!