Two encounters:

-After being asked to change seats I ended up next to a girl and we talked the whole flight. We changed telephone numbers and names and it ends up she was married to my old boyfriend.

-after moving to Hawai many years ago I went to the bank to open up a new checking account for my husband and me. The teller who took care of me said...OMG I lived across the street from your husband when we were little kids.