I'm perfecting my JW-speech, it goes along the lines of "my mother became a JW and it destroyed her life and broke our family apart." (That's true).
Oh that was just a few over zealous brothers whom came to their own conclusions. She said that the org never promoted such a thing.
Make it about the future, not about the past. I intend to conclude with "You are going to grow old and die. I know you KNOW I'm wrong, but that doesn't change the fact that it's going to happen, and by the time you realise it's true it will be too late to have enjoyed your life. How about making plans for you life just in case you're wrong?"