Greetings,
I know that this is going to sound ethnocentric but as a group, they can turn a magical place into a miserable one very quick. If you happen come upon an attraction or area with flag carrying group that are speaking Portuguese ever so loud, turn around and go and do something else. They will do everything that they should not, for example, talking (loud) during films, preshows, attractions. Also, get use to flashes going off during "dark rides" and kids/young adults cutting up in queue lines and attractions.
I believe the problem stems from lack of supervision. There is probably one chaperon for every 50/60 teens. Also, I once spoke to CM about the situation and I was informed of the different classes in Brazilian culture. They as a country don't have a large middle class but rather only the rich and the poor. So the ones visting are either real lucky to be there or feel entitled to do and say as they please. In other words, the CM told me it was a social/economic reason for their behavior .... I think universally it is known as just being plain rude .... no matter what your soc/econ background.
I solved the problem buy going at different times of the year such as Oct. & Jan. Also,wanna see a CM fret & sweat? Tell 'em a group of 75 of the flag people are behind you.
-Chuck
PS.... putting on flame proof suit now. Fire away