You hold it all up in one hand to show how light it is. Sorry, the flight is fully booked. You'll have to check this one, which will never make your connection in Frankfurt. It's often down to the mood of the person at the gate - or your management style. Carry-on luggage looks like being a hot issue in 1998.
Most people agree that hand baggage has gotten out of hand.
Apart from being a nuisance to other people, excess cabin baggage is a safety hazard. Some people use bags as a battering ram to reach their seats. Sitting in the aisle of a crowded 737 you risk being thumped in the face by swinging shoulder bags or your ankles scythed by pull-along luggage. Clearly, what's driving this is that it's a seller's market. The problem is that rules vary widely by carrier, class of travel, type of plane and how heavily a flight is booked, which adds to bewilderment, confusion and apoplexy at check-in.