The vibrations were getting worse. Intensifying. Maybe my nerve endings were getting overstimulated. Worse, my sister was now subtly moving her butt back and forth, as if I wouldn't be able to feel it. Even the fact that we had an audience -- that our driver was clearly checking the rearview mirror way more than was necessary for safety's sake -- seemed to intensify the entire experience.

I clutched Madison's ass. "Stop moving. Monkey. Dear," I said, through gritted teeth.

"Stop feeling. So fucking. Good. Guh-Gator," Madison replied, voice equally restrained.

BANG

We hit a pothole. Madison legit slid right up my cock and straight back down. One fantastic, full...