I had two similar experiences in England of all places. The first time I went, I met this girl who was also from the states, and we chatted and became really good friends. One day, I was talking to my cousin, and it turned out my new friend's dad was his math teacher! The other happened the second time I went, and that time I went with my boyfriend (loooooong since broken up, btw, lol) and we're walking around Trafalgar square, and while trying to take a picture, he literally backs into another girl from our highschool. We didn't even know she was going abroad that summer!