One passenger was left horrified after a woman left a spit-filled cup from brushing her teeth out for four whole hours.
As if flying couldn't get any worse - what with screaming children, the chaos of security and the rankness of onboard toilets - there is now another thing we've got to add to the list.
The last thing any of us want on a cramped cabin, jam-packed with strangers all breathing in the same recycled air for hours on end is to sit with someone's congealed saliva marinating on a seat right beside us throughout the journey.
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The latest on the 'Passenger Shaming' thread on Reddit saw one passenger encounter a severely uncouth dental hygiene fiasco.
The Reddit user posted about her '14 hour' flight to London in which she was sat next to an 'Australian couple'.
After nodding off during the slog of a journey, they woke up to find 'the girl brushing her teeth from her seat'.
"Then she proceeded to spit in a cup, shook the toothbrush in the air to dry it out, and kept the cup there for 4h," the Reddit user continued.
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And the kicker?
According to the disgusted globe-trotter, the toilets were only a mere 'three rows in front' of them and were also 'free' at the time.
And this incident clearly isn't the first nor will it be the last bizarre plane blunder to have baffled a passenger.
One woman was left totally 'flabbergasted' when a fellow jet-setter tickled her leg with their bare feet mid-flight.
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The unlucky passenger uploaded the harrowing moment to TikTok with the short clip showing herself visibly speechless by the encounter.
A passenger behind the woman somehow stretched out their trotters all the way under her seat only to pop out on the other side.
The overlay text read: "I felt something tickle my leg."
She also noted the mystery foot was 'cold' too before adding: "Do you know how far you have to reach your feet to TOUCH the person in front of you?"
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The woman captioned the TikTok: "No way people actually do this I'm flabbergasted."
Oh - and there's many more foot-related faux pas with another passenger getting revenge on a woman who 'kept putting her smelly feet' under his seat onboard the air-tight aircraft.
His response? Simply dripping a smidge of soda onto the woman's feet.
Not too much to cause a ruckus but just enough to get your point across.
Now that's some passive-aggression I can get behind.
Rhiannon Ingle