Sister's got a lot of nerve - first she pees on the toilet in front of her brother, then she strips naked and gets in the shower. But my brother is not a toothbrush - he sees everything and when his sister does that he gets a hard-on. And if he hadn't just jerked her off and walked away, no, she started seducing him. Even if that bitch is your sister, you can still fuck her, because everybody fucks her. What's worse than you? Whoever's closer to the body should get her wet lips more often.
To be a bitch is to get the dogs to do whatever they want. You just have to make eyes at the right time, play with your tongue, expose your nipple. And when he wants more, he'll fulfill any request for her ass.