Most of these not only answer the question, but they also quell the desire to ask any pesky follow-up questions. Two birds, one stone.
  1. "I lost a bet."
  2. "I figured I could be self-righteous and smug about a lot of other things — for free."
  3. "When I was ten, my Cabbage Patch doll came to life, touched my stomach, and placed a curse on me that made me barren."
    Lesson? Don't buy a Cabbage Patch doll at the Goodwill.
  4. "The state won't allow me to have kids."