Avatar The Last Airbender has vicious ship wars, and ridiculous instances of over-sexualized twelve year olds.
Harry Potter has Draco in Leather Pants. And more self-insert fanfics than there are humans on earth.
Nearly everyone on the Modern Warfare/CoDpiece-whatever servers are emotionally stunted, penis-obsessed nitwits.
Also, those kids who read approximately 100 or so pages of Nietzsche and constantly name-drop them in every single gorram class they attend, no matter the relevance or context. I mean seriously, who name-drops Nietzche in chemistry lab?
..... I am fairly certain there are many that are much worse, but I am fearful to tread in the cesspit that they inhabit.
I know someone earlier mentioned Doctor Who fandom, but I haven't seen much viciousness, although I have seen various interpretations of canon that rival PhD theses in length. It's hilarious, although there is a disturbing pre-occupation with using the sonic screwdriver as a vibrator.
OH, I had almost forgotten, several years ago I attempted to explore the section of fanfic.net that contained Soul Caliber stuff, naive youth that I was; I have never seen so many badly written, abuse-addled, horribly justified sex scenes in my life. I cannot unsee the horror.