I mean this in the most kind way to possibly put it: CHILL OUT PEOPLE. You are on vacation....relax a little and stop to smell the roses. Whether that means you have to wait a little extra in line or excuse a fellow human being for something out of control. We all (myself included) need to chill on vacation and just take it easy. It seems we have schedules to meet people to beat and such. The next time we go to WDW we are not going to use a schedule. We are just going to get up and go.
Now on the other hand if 20 people are cutting in line and being disrespectful then I think the cast members can figure that out and take care of the situation. But don't ruin vacation for your kids or other family by making a scene.
Just my humble and kind opinion.
Thank You for saying that. I don't know what I would give to have people "Chill out" like you say. Honestly the people I have met that have one of the
best times in the park are those that just go with the flow and "Chill Out". Wow, those folks really do make your day.
To answer the question. Now, most people that
'cut' the line are either alone or with a bunch of kids and if you guess it's because they had to use the bathroom, then you guess it right. Bathroom issues, count for over 90% of the people that either get out of line and have some one hold their place or join the family later. There is a huge variety of reasons why people do this and I would say that over 80 percent of that 90 percentile by the time, they ask you for the bathroom they are almost ready to do it on themselves. That includes adults. Interesting little piece is that IMO, almost everybody sound embarrassed to either ask for it or to even show that they had to go. Folks, we all go; I don't see what's the problem.
Just in case anyone wonders the reasons for the other 10% it varies and some of them are just too personal of those folks that I wished not to touched upon them, since there is no necessity. Honestly the amount of people that do this because of 'going to do a ride', 'getting a fastpass' or any trivial reason is rather small. The thing is that those are the ones that you remember the most.
As for the OP question if it's rude, here is my humble opinion. I think it's always rude to cut a line. However if you have an emergency (like going to the bathroom, baby issues, etc) and you need to get out of line and someone remains there. Dude, when you get back I'm not going to give you a hard time. I mean honestly most folks would extend me the same courtesy; so why not chill out and let the person go do his stuff and let them pass when he comes back.
Here is something that I always do, when I have to cut a line. This not only to cut some bad feelings, but also out of respect of those of you that had the blessing to calmly remain on the line, while I had to go like a mad person looking for a bathroom. If I cut in line I usually go around 'Excuse, I'm sorry, could I please join my family." No need to give details because I'm usually only one or I have little ones with me. Most people don't need an explanation for why I'm I doing it. You do encounter folks however, that not only that give you a hard time, but also want an explanation... I'll take the 5th on those situations.
Now if you are a group of 20, then you'll need something called organization. One: the lines are designed to hold folks standing one after the other. If 20 folks come in then you are a) Not standing in line, because the lines would only fit one person at a time and the line is probably backed out and, b) Being rude. Two: Cast members are not counting 20 people with you because, guess what? They can't see them. By cutting the line you are literally messing up with the way their operations go, which eventually comes back to hunt you. So if you are a group of 20, I'm afraid that you'll need to organize yourselves better. Stand all in the line and don't send just one, because others are doing a 'ride'. It's not only rude it clearly shows a lack of organization, respect for others and disregard for the rules. I don't hold against you if you have to go to the bathroom or if you have any other emergency but cutting on the sole purpose of not wanting to do the line just shows an abysmal lack of manners.
I don't get upset or emotional about simply saying-
"sir I will not let you pass, I am waiting in line like everyone else. If you have a problem, please go get a cast member and tell him why you need to get to the front of the line. If you have a legitimate reason I'm sure the staff will help you"
Just a heads up, that if indeed the person did have a legitimate reason most cast members will indeed put the person where his family is or will find a way to accommodate them, if the situation allows them to do so. There is no reason for cast members to punish anyone for a legitimate reason. The same courtesy that I'm extending to that person; I will extend it to you, if in need of it.
Pretty simple 
And I am not a confrontational person, so yes, even if someone tried to cut me I would not say anything about it. I might subtly try to block them, but there have been many times in life that people got by me...and I got over it. I won't raise a stink about someone else being rude.
