I guess I'm lucky in the sense that I've never had a bad encounter like those described here at Disney, but on our trip in 2010 I did have one bad experience at Universal.
My father & I were getting ready to enter the "Twister" attraction. We were in that pre-show area where they show the video with Bill Paxton and Helen Hunt waiting for the doors on the right to open so we could go into the main part of the attraction. Well, as soon as the doors opened, this little teenaged punk (I remember noticing that he was wearing a ridiculously large t-shirt that hung to his knees and made him look like he was in a mu-mu) decided he needed to be the first person in there, and literally shoved my father - who's in his mid-60's - out of the way and down onto the steps. Didn't apologize, didn't even slow down for a second and look back. I helped him up (along with a couple other concerned and very kind park-goers), he was ok, and we went in, but suffice it to say at that point I didn't really get any enjoyment out of the attraction because I was so furious over what had just happened. When it was over, since that kid had been the first in, he was also first out and I didn't see him when we exited. I calmed down and we enjoyed the rest of our day there, as well as the entire rest of the trip. But I just hate that something like that had to kind of "stain" our day, ya know? But as people have said, rudeness is everywhere so I guess you just have to prepare for it.