Few would call airline travel an enjoyable experience. To be confined in the smallest, least ergonomic of spaces, breathing the same recycled air as hundreds of strangers for hours on end can drive even the most sane, even tempered individual a little batty.
Take a recent United Airlines flight. Enroute from Newark, New Jersey to Denver, Colorado, it was re-routed to Chicago, Illinois, after two passengers got into a heated dispute.
One of them had used a Knee Defender, a US$22 (S$28) device which prevents the passenger in front from reclining his seat. Insults were exchanged, a soda was hurled and both passengers were discharged from the plane and barred from continuing their journey, though no charges were filed.
Mr Trevor Gilmore, 28, an American intercultural consultant who teaches people how to work and communicate in unfamiliar cultures and situations, says passengers must simply face the reality of air travel and focus on the positives, not the negatives.
He says: "I've flown about 56,300km this year and frankly, my pet peeve is when people complain about minor things such as other passengers reclining their seat or leaving their lights on.
"People need to be polite and considerate and remember that they're essentially on a sky bus with TV, food and pretty clean toilets."
Unfortunately, it may be easier said than done. Airplane passengers are quick to anger when their space and senses, particularly those of sound and smell, are encroached upon.
SundayLife! talked to dozens of frequent flyers to find out what their top 10 in-flight pet peeves are.
The No. 1 complaint of travellers everywhere is the dreaded crying baby. While most passengers are understanding of the trials parents face when they have a baby on board, there is no sympathy for parents who choose to practise tough love 9,000m in the air.
Consultant Ethan Tan, 36, cites a recent flight from Singapore to London when a child was crying uncontrollably to get his father's attention.
"The father just focused on his in-flight entertainment and refused to pacify the small child. He was trying to wait it out, it seems.
"That led to the child raising his volume for attention and it just went on and on. It became a contest of willpower. Passengers had to call in the cabin crew for intervention," he recalls.
In these cases, the parents' reactions to the crying or tantrum-throwing child are key.
"Yes, you are probably frustrated as a parent in that situation. But the decision to bring a child on a flight was yours, and he or she is not hand luggage to be stowed away and retrieved only when the plane lands.
"With a fussing child, I'd like to think that passengers are empathetic if you are really trying," adds Mr Tan.
Sometimes annoyances can begin before boarding. One of the frequently mentioned pet peeves is people who do not know the basic rules of airline security: no liquids more than 100ml, laptops or tablets taken out of bags, shoes and belts taken off, pockets emptied.
Some passengers are also irritated by those who give improperly or unfilled customs and immigration forms.
"It's probably my biggest pet peeve because it kills me when I'm behind them in the customs line and they hold everyone up," says executive assistant April Lee, 28.
Meeting new people and exchanging life stories is best saved for a networking event, not a long-haul flight to Frankfurt.
It is the main bug bear of jewellery designer Carolyn Kan, 42, who enjoys keeping to herself on long haul flights. "Flying is when I get my best ideas, so when other people want to talk, I find it quite bothersome. I put on my headphones and make a comment about the film I'm watching and hope they get the message," she says.
Poor hygiene is a big turn-off in general.
One of the first things most passengers do as they settle into their seats is take off their shoes and socks. This is all well and good, as long as your feet are clean.
Ms Choy Teh, 33, public relations specialist for The Travel Corporation, a collection of international travel and tourism companies, says it is particularly bad when travellers put their feet next to fellow passengers.
"I hate when you have a window seat and someone props their foot up on the side where your armrest is and you can see their toes in full view. All you smell is rotten cheese the entire flight. It is selfish and rude," she says.
DISGRUNTLED FLIGHT ATTENDANTS
Writer Tara John, 27, hates encountering rude or inhospitable flight attendants, particularly on non-budget flights.
"Not only have I paid more than $1,000 to travel on their airline, I also have to assuage the temper of an overworked air hostess who is acting like I have disturbed her day by asking for some water, which is her job to provide," she says.
Passengers who are rude, arrogant or aggressive towards airline staff also raise the ire of frequent fliers, particularly if they have had too much to drink.
Mixologist Ethan Leslie Leong, 38, particularly dislikes seeing passengers taking advantage of free in-flight alcohol.
"It's like they have never had a drink before. Then they get drunk and sometimes will sing and talk loudly.
"Some even start jumping around and dancing, or pressing the service button every minute asking for more drinks to be served and they can become aggressive. It is quite annoying," he says.
ENCROACHING ON PERSONAL SPACE
Every centimetre of space counts when you are on a plane, which is why any attempt to claim more of another passenger's space is a no-go.
"It is so irritating when there is a person sitting beside me who keeps nodding off and pushing his or her body on me, or keeps taking up the arm rest. It's an invasion of personal space," says student Vicky Chen, 23, who flies about 10 times a year to visit family in Europe.
Arm rests are contested territory best left to the passenger suffering in the middle seat. Let them have the one perk of two arm rests, at least.
Anyone who has ever been on a commercial airline knows that seats must be returned to their upright position during take-off, landing and meal times, when eating can prove difficult with someone's headrest 15cm from eye level.
But some passengers ignore this.
"It annoys me when people keep their seats reclined when meals are served. It is so inconsiderate," says senior events manager Nadine Ismail, 27.
When dozens of people share the same lavatory for a few hours, it is bound to get messy, but that does not mean that every passenger cannot do his part to keep it as clean as possible.
Frequent flyer and creative director of craft and artist management firm The General Company, Mr Colin Chen, 31, says he is frustrated by people who mess up the lavatories and do not try to clean them up.
"A little initiative and some basic courtesy can go a long way to make everyone's flight more enjoyable and bearable.
"I think everyone should have the basic responsibility of keeping the planes clean, and to be considerate of other passengers," he says.
Airlines charging for check-in baggage means that space in the overhead compartments is precious real estate.
Passengers tell SundayLife! they are frustrated when they arrive at their seats to find the overhead compartment already full, particularly when it is filled by people who are not sitting in their row or when the luggage is improperly stowed.
"I feel that if the flight is shorter than six hours and you are less than 1.8m tall, there is no reason for your backpack or coat or small item to go in the overhead rather than by your feet," says financial research associate Alexandra Chan, 29.