These groups sporadically show up throughout the year (I've definitely seen them around in February and March) but July is when they come out in full force. I tend to avoid the parks during the summer due to the large crowds and awful heat (and I'm a native so I'm used to this weather!).
Anyway, here are some of my tips for dealing with them (them being any large group of people who may do something to bother you):
-always make a note of the nearest CM. If you are unfortunate enough to have 30 people 'cut' in line in front of you, have one person from your party go to the CM. Some CMs won't do anything, but some will be just as fed up and not allow it (I've seen that happen a few times). As long as you're nice, polite and sympathetic to the CM, it can't hurt. You might just get fast passes out of it but hey, that's something!
-don't give them attention! I've noticed that the more people watch them, the louder they get and longer they go on
-if you witness anything offensive to you, report it! Security has taken action when large groups do things such as flashing, etc. You don't have to deal with that.
I hope that helps some... it applies to any large group that forgets their manners since people tend to get more obnoxious when surrounded by friends
I probably didn't say anything new and useful though but it was an ice vent lol