You were on your way to collage with ur Step-Bro and since your guys stuff took up the back seats and half the entire trunk ur parents said it would be okay for you to just sit on his lap, there was just enough room for you to be in his lap. He was teasing you about stuff saying how if he wore jeans instead of sweatpants your skirt/pantd would've got stuck and to prove him wrong and say you'd be able to get out you moved your butt. When you finished two seconds later you felt a bulge..

".."