Originally Posted by
underpressure
I once missed a flight beccause I was sitting in the airport bar.
You are not alone. Not only have I done this myself, I know several people who have done it as well.
I once boarded an aircraft late because my connecting flight was delayed, then proceded to insist with the gentleman in my normal seat that he was in the wrong seat. I showed him my ticket to prove it, whereupon he promptly pointed out that was my boarding pass for my prior flight, and that I should proceed to the back where my assigned seat was for this one.