Last week I was flying a redeye from SEA to MSP. The flight was completely full and they made multiple offers to check bags. Then there was an announcement that if you attempted to board with more than 2 items, they would automatically check anything over the limit.

As people were boarding the FA directed each person to place their second bag under the seat as he figured they'd run out of space in the overhead. A passenger boarded and began to place both of his items in the overhead. The FA asked him to please hold on to one of them. If there was still room, he could place it in the overhead later.

And then the whining began. "Look, I fly ALLLLLLL of the time". "This is ridiculous." As other passengers boarded he started complaining to them. "That flight attendant doesn't know what he's doing" The FA asked him to please try and place the bag under his seat. The passenger stood up and started saying that he's sure it won't fit. "See, it won't fit. Ugggggghhhhh" We all listened to him whine until the FA finally just said to place it on the overhead.

And, of course, as the last passenger boarded they ran out of room. The last to board had to check his bag.