People taking the piss with carry on bags
If you've been on a flight lately, particularly a short haul flight, you have probably noticed that really annoying scramble that a lot of people do to try to be the first person on the plane. I've never understood why people are so excited to leave one small seat in the terminal, and then rush to go and sit in an even smaller one in a metal tube.
As it turns out this scramble is most likely because there isn't enough storage space inside the plane for everyone's bags and they want to get theirs in there at the expense of someone else not being able to.
I don't design planes, but you don't have to look all that hard to realize that there is probably JUST ENOUGH space for everyone to have a small suitcase and that's it.
But these days it seems like people are really pushing the limits as far as their carry on bag is concerned and this selfishness has lead to other people not having any space for their own. I'm kind of surprised that no one has ever tried to use the space under my seat to store their bag instead of their own space.

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Years ago it was unusual to spot people that would have a bag that is definitely pushing the limits of bag size allowances and then a gigantic "personal item" that you would fit 2 bowling balls into, but these days that is basically everyone on the plane.
I think airlines are to blame mostly for this because they kept jacking checked bag fees to the point where everyone is doing everything they can possibly do to avoid checking a bag at all. Just like most things, it all boils down to money and greed. When Spirit Airlines went out of business I kind of rejoiced. Those clowns were awful for charging you something crazy like $100 for a regular sized bag to go on your flight that cost $80.
But I have noticed when I fly these days that people are taking the piss more and more with their carry on's and they seem to do this in an almost shameless manner.

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I'm part of the backpacking culture. I was there near the start of it, but the fact that so many people think that they can and should be able to shove this monster above their seats is absurd. Airlines have begun cracking down on this and when I see someone start to argue back I wonder what they are hoping the end result could be. The customer is rarely "right" in these situations.

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Then there's these people: Enormous backpack on the back, smaller one on the front that is normally full, and then a "fanny pack / bum bag" tied around their waist.
Another instance I saw was of a rolling suitcase that was already pushing the limits of dimensions but it also had these punch out sections on the top of it that went several "floors" to the point where the bag was nearly doubled in size. The guy got flagged and told he had to check his bag. He protested, and the lady behind the counter had to tell him to calm down and comply or he would be denied access to the plane outright.
It's a shame that it has to be like this and initially at least, the airlines are to blame, but the attitude of some people who are trying to bend the rules, even when success at doing so means they are going to inconvenience other travelers, you people are not better.
Here's an idea that I think every traveler should take to heart: Stop trying to bring all your worldly possessions with you when you go on a trip. They sell toiletries and t-shirts in every country in the world, you do not need to bring your entire bathroom with you when you travel. In fact, you will probably discover that you don't end up using most of what you bring with you anyway.
When I travel, I pack all the things I cannot live without such as my electronics and then I will pack all of my underpants. And that's about it. I never have any trouble with bag sizes at the airport and I never feel the need to make that mad scramble to be the first person on the plane either. Do you want to be stressed out?