I think the flaw in your thinking is that you seem to believe that 'rude' and the opposite 'civilized' actually still apply to air travel. The simple observation of how people crowd in front of the boarding area before every flight, should indicate to you that your expectations are not in line with reality.

I think there are also two other factors at play here. One is culture. In some cultures, 'lining up in an orderly fashion' is simply not the norm. That person walking in front of you may not be doing anything 'rude' at all in their view and it is their view that determines their behaviour, not your view.

Second, why not look at the underlying reason for why people want to rush the gate? Do you really think it is because they just want to get on the plane and sitting in their seat waiting for everyone else to be seated for take-off? No, that is not why they want to get on board first, do I really have to say it is about overhead bin space? I sometimes think that the best way to handle boarding would be to call Y class first and First class last. That way, you can sit and relax, read a book or whatever and then 'stroll' on board without having to deal with any hassle at all. No need to put up with 'rude' people with no more status than yourself 'butting in' line in front of you. I much prefer approaching the gate when there is no line at all. Just before the gate closes in other words. I do that regardless of what class I am flying in. So far, my seat has always been waiting for me when I got to it.