This text message exchange represents a kind of joke that is imminently easy and lazy in a "that's what she said" kind of way, but is also irresistible to almost every funny person I know.

"That's going to be the title of my autobiography."

"That was my nickname in high school."

"Wasn't that the title of your band's first album?"

It's an almost compulsive response to an unintentionally evocative (or yes, just dirty) turn of phrase. They're not even jokes, really. I think it's mostly a way of saying, "I like those words together." Taking someone else's sentence and florescent yellow highlighting the part that tickles us.