When I moved from STL to LA, I was on Hollywood bus when I bumped into an ex-girlfriend from home (with 6 million people, what are the odds)? But wait, there’s more–later in a different part of town, I bumped into ANOTHER ex-GF from home! I should have played LOTTO.
Facebook just reminded me of one today…
I went to a Catholic high school in the Archdiocese of Baltimore, and the archdiocese used to sponsor these week-long summer retreats they called the High School Leadership Institue (or “High-Li”). If you had/were going to have a leadership role in your junior or senior year, a faculty member could nominate you to attend. I went in the summer of 1988, with a bunch of kids from all over. It was a great experience, but I didn’t keep in touch with anyone.
Flash-forward 27 years to 8/22/2015: I went to the funeral Mass for an old friend’s mom, and the moment I stepped into the church a woman who looked familiar to me said “you look familiar…” During the repast, we figured out that we went to the same High-Li! 
Turns out she was also good friends with the guy whose mom had died, and had also known him for decades, but our paths had simply never crossed before.