The mere mention of the Furry WebcomicJack is sufficient to earn a permanent ban on some forums. It is THAT controversial.
Similarly controversial is Dominic Deegan. Mention any of the following—Stonewater, Snowsong/Supergreg, Siegfried, Klo Tark, whether Luna is a Mary Sue (or indeed all of the characters), the art, the writing, Mookie himself—and there will be an explosion of unrivaled proportions. Needless to say the Fandom and Hatedom are both strongly developed and don't show any sign of backing down.
Much like the above examples, mere mention of the Sisterhood Arc in Sinfest is just asking for trouble.
Homestuck. Merely mention Homestuck anywhere outside the official forums is enough to start a full on brawl due to the massive amount of Fan Dumb it has caused over the years.
The general fandom for Las Lindas are basically gas soaked kindling waiting to be ignited. Rarely a page went by without the comment section erupting into a Ship-to-Ship Combat discussion, Fan Dumb trashing and White Knighting of the characters featured, and a few general Trolls lingering to start trouble. This led to the comic comment system being shut down.