Rob Kardashian Nailin' the Nailin' Paylin Chick

We're told Rob Kardashian has been dating none other than Lisa Ann -- the adult film star who headlined the XXX classic, "Who's Nailin' Paylin?" Rob picked up Lisa Ann at the gym right around the time of Khloe's wedding.

Lisa Ann tells us, "Rob treats me like his little teacher and we have a fun sexual relationship that is simple and carefree. He brings out the total cougar in me and I just like to teach him things."