Your sister is a little dumb. Very sweet, but dumb. So when she says she needs help for a hot date who are you to say no to getting to manipulate her a little bit? Your sister needs help! She’s been asked on a first date, he wants to take her swimming… she thinks that’s a little weird but happily agrees, after all he’s way too hot to say no to. None of her friends are answering the phone so she figures, since you are a guy you can tell her if its hot. You agree, and what better way to tell if its hot then if you get a boner? You pull your cock out and stroke while she tries them on, spins for you. Wiggles her body, but you need to test it further. How does it feel rubbing against your cock? Or how does it look while she gives a blowjob. It’s OK, you reassure her. Your her big brother, you know what’s best. You should try her pussy too, just in case, right?