You've been up since 3 a.m.
After dealing with long check-in lines, long security lines and long faces from flight attendants even unhappier to be on that plane than you, your 6 a.m. flight finally lifts off.
"I'm just going to recline my seat and catch a couple of hours of sleep before we land," you think as the pilot switches off the seatbelt sign.
The Knee Defender has caused three flights to make emergency landings in just over a week. CNN's Tom Foreman has more.
The fight over seat reclining has led to multiple flight diversions. James Beach explains why he used the Knee Defender.
But wait. What's happening?
Despite pushing that little round silver button and digging your heels into the floor, your seat refuses to budge.
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You've just been blocked by the Knee Defender.
The 2003 invention of 6'3-tall American Ira Goldman -- "I was tired of being bumped in the knees by reclining seats" -- the Knee Defender is a small pair of plastic clips that attach to your lowered seat-back table, locking the chair in front of you in place so the passenger can't recline.
Proof of its contentiousness came out this week when United Flight 1462 from Newark to Denver was forced to divert to Chicago's O'Hare airport after a fight broke out between two passengers over one's use of the device.
Despite the passengers getting kicked off the plane, the story has led to a boost in sales of the Knee Defender, with the website even crashing under the weight of all that curiosity.
Is the Knee Defender even allowed?
The U.S. Federal Aviation Administration says it hasn't banned the device as it doesn't have an impact on passenger safety.
But most major U.S. airlines, including United, do prohibit its use.
It's a similar situation elsewhere.
"You are not permitted to attach any unapproved device to any part of your seat or any other part of the aircraft," says WestJet.
"Some examples of unapproved devices include knee defenders, seat belt extensions and booster seats."
Same story in Australia, where carriers Qantas and Virgin have reportedly banned the device.
"The use of knee defenders or similar device would be in breach of our conditions of carriage (14.2 (b)(f)) which are available on our website," a Virgin Australia Airlines spokesperson told CNN.
"The safety and comfort of our guests remains our highest priority."
Singapore Air told CNN the crew would manage the use of the Knee Defender by customers on a case-by-case basis.
"We are reviewing the use of the device, though we have not received any feedback from our customers," said an airline spokesperson.
In the case of this week's United inflight battle, the flight attendant reportedly told the man to remove the Knee Defender device, but he declined.
The female passenger then threw water in his face.
The inventor is adamant that buyers should be considerate of other passengers when using the device, which costs $21.95.
Users of the device are even advised to print the Knee Defender courtesy card, which explains to the passenger in front of them that their legs are so long their knees will be banged if the flier's seat is reclined.
"If you would like to recline your seat at some point during the flight, please let me know and I will try to adjust myself and my Knee Defender so that it can be done safely."
To recline, or not to recline
The incident has brought to the fore the usual comments on plane etiquette.
Some say such devices infringe on passenger rights.
Simply put, if an airline allows offers a reclining mechanism -- and some low-cost carriers don't -- then tough luck for the fellow behind you.
If he/she doesn't like it, they should cough it up for an upgrade or request a front row seat upon booking, citing their long legs or an injury that requires extra room to stretch out.
In the case of United Flight 1462, the pair was seated in the Economy Plus section, which provides passengers up to five inches of extra legroom.
Others say passengers need to be respectful of fellow fliers.
"I don't think any of the seats should be able to recline in economy," commented David Cleland in our article on the United dust up.
"I have tried to work with someone in front of me reclining and bouncing around. It really is infuriating. I have tried to ask the person in front of me to please not recline...I might have just spit in their coffee by the reaction I received."
Then there's the issue of flight time. Is it really necessary to recline your seat on a two-hour daytime flight? How about a red-eye cross-Atlantic journey?
Others -- including Knee Defender inventor Goldman -- blame the airlines for pushing us to the brink by taking away all our space.
So how would you react to being told you could only recline your chair a distance designated by the person behind?
Should airlines do away with reclining seats altogether?
Share your thoughts on the issue in the comments section below.