This is after an opinion opener and perhaps some conversation/fun and games/asking how they know each other. I've seen some posts like this one:
which say that you should just say "Oh that reminds me...." and start your story.
Problem is, people just go (or act as though they're thinking): "Uh, why are you telling us this [story about your ex, whatever]?"
So how do you actually transition with a plausible reason?