At WDW a couple of years ago I told DH to take the kids and I would meet him by the entrance of the carousel--I parked the stroller, went over to the line, only to find out that he had alreday entered the line and there were about 20 people separating us.
I didn't get in line--because that would have been RUDE to pass by all those other people, instead I left and watched from the side.
A party should never split up and get on line and expect to think it's just fine for the other people to squeeze by evryone else to catch up. If my kids can't wait, they can't go.
It's rude and inconsiderate.
I would never say anything to people who do this sort of thing because that's not my style, but I do notice and I don't like it at all.
If someone needed to leave the line to take a young child to the bathroom, that's fine with me-though my daughter is asked if she had to go before we get on line..if she tells me she has to go mid line, I ask her if she can hold it, she would normally say yes, if she didn't we would get off the line and get on the back when we were done because I would not be comfortable pushing past everyone.
As for getting out of line to get drinks-

I'm pretty sure that's not an "emergency".