You can see the nervous glances on any flight when the seatbelt light is pinged off, as each passenger anxiously wonders: "Do I have a recliner in front of me? Are my precious seven inches of legroom safe?"
Incursions into personal space are a familiar source of aggravation at high altitudes. So it's not surprising that, according to reports, a United Airlines flight from Newark to Denver was diverted when a passenger prevented the woman in front of him from leaning back using a $21.95 (£13) lock called a Knee Defender. The plastic clips go on the metal arms of the tray table, physically preventing the seat in front from being reclined. The clips come with a card that can be given to affected passengers to explain the motivation of the user.
After the passenger allegedly refused requests from cabin crew to remove the Knee Defender, the un-laid back fellow traveller in front allegedly hurled a glass of water at him.
The man's methods may be extreme, but some travellers - unable to work on their laptops, eat, or simply enjoy the meagre proportions of economy class to the full as a result of leaners-back - will sympathise. For some time now, a backlash against reclining has been under way.
Earlier this year, a frequent business traveller's call for a "revolt" against reclining seats went viral. A survey by Skyscanner in 2013 suggested nine out of 10 travellers wanted to see them banned. Another poll for CabinCrew.com indicated that more than 60% of international cabin crew had observed an argument between passengers as a result of them.