Jerry Jeff says, "Think about it, Darlin'" at the end, parodying Jerry Lee Lewis. He doesn't say "Sit on it, darlin'."
Also, wish we could find definitive Chuck Pyle lyrics. He wrote it. And wrote it as a much more tender song. Jerry Jeff did make some lyrical and melodic changes. Nothing too drastic. Jerry Jeff's version is more snide, more vengeful, and, within that, funny.