Our whole family is on vacation together in a rustic mountain cabin. step-Mom and step-Dad have decided to visit the little town down the road, but you and I just want to chill in the hot tub--but you seem to have forgotten your swim trunks. I say it doesn't matter if you come in naked, but I'm also wearing an incredibly slutty little micro bikini. You don't want to say anything, but you're worried that you'll get hard. I start teasing you saying that I probably wouldn't even notice. You assure me that I would. Finally, I propose a bet: if you are, indeed, poorly endowed, I get to choose the next family vacation and you foot the bill. If you do have a huge dick, I'll pay for the family vacation that you want. You agree and drop your pants. ... I can't believe it. No wonder you're always slouching! Your dick is gigantic! I start encouraging you to get hard, stripping out of my already tiny bikini and fingering my ass. I don't care if you are my step-brother, I want to see how much cum that enormous cock can make