When you find the neighbor's wife sitting in your backyard by the pool.
Jack: "Uh...Mrs. Farley? What are you doing here?"
Mrs. Farley: "Oh shit! Jack! I thought you were at school...I'm so sorry. We don't need to tell your parents about this, right?"
Jack: "I don't know, Mrs. Farley. I guess I could be persuaded to keep quiet..."
Mrs. Farley: "<sigh...> Fine, but just this once and this stays between us, got it?"
Jack: "Sure Mrs. Farley. If you say so...."