Came across this and my queanbrain immediately latched onto it.
Imagine being a daughter of a total boobmonster, waiting for yours to grow in but they never do. Fed up with the chestlet life your mother has condemned you to, you decide that if she wont give you what should rightfully be yours, you will take what should rightfully be hers; you decide to seduce her husband. The whole endeavor turns out to be rather easy, after just a few weeks of hidden flirtation and stolen kisses you have him eating out of your hand. You guess that you must be a master seductress, or your mom isn't giving him enough attention in bed. You decide that it's time to really seal the deal, so after managing to get mom out of the house, you jump his bones. You're riding him raw, having a great fucking time, riding extra high off the fact that you're stealing him from her. He grabs both your hands and says "Honey, I'm getting close." Huh, that's kinda weird, why would he grab both your hands, and he always calls your mom honey... Suddenly, you feel feel hands on your hips holding you down as a massive pair of tits push into your back. "Silly girl. Did you think I didn't see what you were doing? If you wanted to get pregnant so your tits will finally sprout, you only needed to ask." You hear your dad moan, then feel his dick start to twitch as he shoots his load into you, all the while your mom is holding you down and making sure every drop lands inside you, voicing her encouragement to him the whole time. When he's done she removes her hands from your hips, then swats your butt lightly. "If that round didn't take, we can try again next week. Now move it, I'm going to clean your father up and our vixens don't get to be here for that part. Be sure to close the door on your way out, and don't forget that dinner is at 6." In a well-fucked stupor you meekly pad out of your parents' room, the sound of your mother sucking your juices off your dad's dick ringing in your ears.