"Well, Sam, I'll tell you how it is. You see, I married a widow, and this widow had a daughter. Then my father, being a widower, married our daughter. So you see, my father is my own son-in-law."
"Yes, I see."
"Then again, my step-daughter is my step-mother, isn't she? Well, then, her mother is my grandmother, isn't she? I am married to her, am I? So that makes me my own grandfather, doesn't it?"