Flight attendant shows why your reply to them saying 'hello' is very important

It's an introvert's worst nightmare when you're hopping on a 6am flight and you get a 'hi', 'hello' or 'good morning' when your brain and social battery haven't woken up yet.

But if you've ever walked onto a plane and been greeted by a flight attendant, it's apparently not just because they are being friendly - even though the large majority are.

As they ask to take a look at your boarding pass, you might notice them giving you a quick scan up and down.

And no, it's not because you're hot stuff (even though you probably are).

Actually, they're scanning you to check that you're not a safety concern because, if you think about it, a lot can go wrong when you're 35,000 feet in the air.

There's many reasons why flight attendants greet you on a plane (Getty Stock Images)

In the event of emergency, passengers and staff will need to be switched-on enough to act quickly if needs be.

Wizz Air flight attendant Iona Iachim posted about this topic, saying that the greeting is 'to check whether or not you are too drunk or sick to fly'.

Also, according to flight attendants who responded to a Quora thread some years ago, a person with 30 years of experience said turning up drunk on a plane means you're automatically a safety concern.

"If a guest coming aboard is drunk or intoxicated by any drug, it can happen that he or she is not allowed to enter the plane," they said.

Flight attendants are always scanning (Getty Stock Images)

"The first impression is often the right one, and we do refuse passengers who might be a danger for the safety of that flight.

"So far I have refused four passengers and was luckily backed up by the purser and captain. All of these were drunken passengers."

A person who had been a flight attendant for 27 years explained: "Air travel is fraught with inherent danger — one must be constantly alert and aware of one's situation.

"So when I greet people, you better believe that I'm always very aware of each passenger who steps through the door of the aircraft."

Airline staff need to make sure you are not a safety concern (Getty Stock Images)

Other airline staff say in the event of an emergency evacuation, the last thing they want is passengers who are unable to follow clear instructions.

"If we may need to evacuate the aircraft, the goal is to do so in 90 seconds, and I don't want to unnecessarily risk my life or the life of others because a drunk or high person is being uncooperative," one admitted.

Equally, if you're 'muscular' or 'strong' looking, flight attendants will keep a 'mental note' where you are sitting on the plane.

Gym bros assemble!