Suggested by Shaker Brenda A.: "What is a strange coincidence that has happened to you, or that you have witnessed?"
One of the strangest coincidences that ever happened to me started in a book club chat room circa 2000. There was a dude who was having technical problems as he was trying to join the chat room, and he was asking for help in a most hilarious way, and everyone else was ignoring him, so I private messaged him to try to provide some tech support.
After we managed to solve whatever problem he was having (I can't even remember), we got to chatting and became friends. He lived in Nottingham, England, and I was living in Chicago at the time. After a few conversations, he mentioned to me that his best friend since childhood had moved to Chicago. He started telling me about him, and it turned out that not only did I know his friend's wife (!) but that his friend DJed in a club directly across the street from my apartment. (!!!)
That has to be the biggest "small world" coincidence I've ever experienced.
A couple of years later, Iain's and my last stop in the UK before we headed back to the States for good was at that bloke's flat in Nottingham. :)