The BRAZILIAN TOUR GROUPS - they pretty much have January on lock. My best advice is to avoid the parks they are at but that is pretty hard to do. I had the pleasure of being there this past January from the 1st until the 15th and the tour groups were HORRIBLE. They were loud, obnoxious, cheered every second. My experience with the groups is that they think they own the theme parks when they are there and are very arrogant. I cursed out a group of brazillians teens in portugese (they had no idea I spoke it) because they were making fun of my boyfriend and I. I made them cry - it was lovely.