I have never seen this happen during flight, but it occurred to me that it could be possible. Have you ever seen the captain come around during the flight to chat to the passengers, shake their hands, etc.? United has some pretty old-school guys up front, so this is not out of the question IMO. I'm guessing this went out during the 70's or 80's (after the advent of mass travel with the 747 and deregulation), but curious to see if anybody still sees this charming, hospitable gesture from time to time.