When someone farts into another persons butt. The other person mixes the fart around inside them, then farts it back out. It is a fart within a fart.
Sharon: "baby, I want us to move our relationship to the next level...I think we should create something together."
Ben: "I love you Sharon, but I don't think I'm ready for kids yet."
Sharon: "kids!? No! I want us to make an inception fart!"