Misty comes home earlier than expected from the pool party. Apparently her boyfriend Mark partied too hard and couldn't get his dick hard. She's super pissed and horny since she's been cock blocked twice today. I tell her i'm about to go head out to watch the fire works at the farm we used to go to with the family when we were younger. She seems to perk up and asks if she can come with me. She grabs some snacks for us and we head out. We take dads truck to the fireworks and when we get there Misty pulls out the food she brought, I ask her about the random cucumber in the basket and she holds it up, staring at it and says it reminds her of Marks dick. She starts to suck on it which immediately makes my dick hard even though I know she is being crazy. Then she pulls her swimsuit to the side and starts fucking herself with it in the back of the truck!!! My cock is rock hard now through my pants and she notices and says she wants to see if my dick is as big as the cucumber. She pulls it out and next thing I know she is sucking it and then getting on it! She rides me and I can't hold back seeing her ass bouncing I quickly feel like I am going to cum. I tell her she needs to get off but she keeps going!!!! I can't hold back and beg her to get off me but she won't! So I cum inside my big sister. I hope shes on birth control....