Missed a few due to late connections but only 1 that I can think of that was my fault.

I was flying HKG to Shanghai and used the Airport Express downtown check-in. When I went to check in, the agent told me: "You're too late Mr. B, the flight is leaving very soon" Me: "Oh no it's not, it doesn't leave until 4p.m." Her: "No Mr. B, that is when it arrives in Shanghai, it leaves in 10 minutes..."

Fortunately managed to switch to a later flight that day.

I almost missed one due to not hearing any gate announcements (I'm still not convinced there were any...). I was on a puddle-jumper from LGW to Maastricht via Eindhoven and it had about 24 seats on it. I was sitting in the terminal as they probably were starting to close the doors and noticed my watch. I ran to the gate but didn't see it and thought I'd missed it. No, it was too small for the gate so I had to go down the steps and across the tarmac. I was definitely the last passenger on the full flight and had to walk down from the back of the plane to my seat at row 1 past all the other passengers who had been waiting for me - very embarrassing! Not helped by the fact that I was carrying a duty free bag so they knew why I was delayed...

I also did it the other way on an earlier flight from HKG to Shanghai for an overnight trip. I checked in at the airport with some colleagues and the gate agent told me "Mr. B, your flight is not until tomorrow". I managed to get on that flight but since then I've always checked the date on the tickets carefully!