I have been looking all over for a story from I think years ago and I just remember the beginning plot. The brother answers the door and the sister's friend has left her bikini at the house, but he informed her that his sister and parents went to the beach that day. She comes in to grab her bikini, but on the way out as she's changing into it, he sees her reflection in the mirror and then she tells him not to come any closer and then he says please show me yourself and when he does, he ejaculates so hard that he passes out and she escapes, but calls waited that night to make sure he's alive and she goes on to tell him that his sister is into him.