Rudeness knows no age but it's shocking how younger and younger kids are that are okay with cutting loose. I blame the parents and adults around them who allow it.
When in my home my neighbor kids have to be kind to each other, not tattle and not be mean or I send them home. If they 'demand' something I say, "how do you ask for something?" I'm trying to teach them the proper way to do things...and 99.9% of the time they comply...I think when an adult takes the time to show a child the right way to behave they appreciate it. Of course, teenagers are a different story, but still...NOT saying anything when they do something is telling them it's okay to (fill in the blank). I guess I'm old school. I sent a neighbor kid home the other day because she would not listen to me and kept wanting to argue...that doesn't work around Ms Dee...she's getting better...it takes being persistent and letting them know that rudeness isn't going to wash.
Once they're grown...some people do it as a shock factor I think and to 'prove' they're grown and can do what they want...what they're really doing is showing how immature they remain.
Just my ever-so-humble opinion.