As typical cabin baggage swells to elephantine proportions, space in overhead lockers is increasingly at a premium. But, while a modicum of common sense from passengers would go a long way, airlines must shoulder some of the blame.
It starts when you catch the enemy's eye. A sneer, a hunching of the shoulders and you tighten your grip on your 'weapon'. You step one way, feint the other and dive for the gap, elbows out, head down in the style of Zinedine Zidane, feet flying as you claim the prize: a square metre of fresh - well, recycled - air that's yours for the duration.
This is no Wan Chai stand-off; no police-versus-South-Korean-farmers fixture on the road to the Convention Centre. It's the sort of confrontation that takes place every day in economy-class airline cabins.
Even when passengers aren't literally facing off they are still, in a way, fighting for control of the overhead lockers by grunting, heaving, pushing and shoving heavy, over-packed bags into restricted spaces, making sure their precious non-cargo cargo is securely stored, even if it is at the expense of everyone else's (or, in the case of the Cathay Pacific Airways passenger on a recent Hong Kong-Tokyo flight who refused to place her Gucci bag underneath the seat in front of her, delays take-off for an hour).
This pre-flight scrum is a regular occurrence because the amount of carry-on luggage taken aboard aircraft has increased in proportion to the prevalence of air travel. Statistics are few, but more people flying every year plus more money to spend every year equals more stuff bought to take home from Phuket and less space on the plane in which to stick it.
Newton's fifth law of diminishing ticket returns says that the less space available, the bigger the bag one tries to cram into it. This, airlines realised long ago, leads to delays all the way from the carry-on baggage scanner to the overhead lockers to the runway. The bigger the bag, the longer the scan, the more detailed the manual search at the end of the conveyor belt, the longer it takes to reach the gate and the more time-consuming the frantic search for stowage aboard the aircraft. In a cutthroat market this is particularly bad for business; planes don't make money unless they are in the air and fast turnarounds are in the airlines' best interests.
So, is there a carry-on crisis aboard aircraft? In 1998, the Association of Flight Attendants petitioned the United States' Federal Aviation Administration (FAA) to enforce a maximum size for carry-on bags because flight attendants were having to mediate in passenger disputes regarding stowage. The FAA refused and passengers, largely ignoring the sort of test-your-bag-here glass receptacle found in airports as well as MTR stations, continued to feed steroids to their carry-on luggage as a means of beefing up their allowance. Carry-on bags with wheels - although by definition they are no longer carry-ons - make it easier for passengers to lug extra loads to the gate and once on board, a crew member can be relied on to take the strain and lift such a bag overhead. It's certainly not going to fit under a seat.