I was once flying ORD-LHR F on AA. About 20 minutes into the flight, a man rushed the cockpit and was tackled by FA's and passengers. His father raced up and said he was a severe diabetic and when he has hypoglycemic attacks he has sometimes become delusional and violent. After a glucose tablet or two, he returned to normal but captain kept in in F so that FA's could keep a better eye on him. My comment was: "Oh, so that's how you get upgraded to F." The feeble attempt at humor was not appreciated.