Ron the death eater 

The polar opposite of (and often directly caused by) draco in leather pants, whereby fandom demonizes a previously likeable, good character, often for the sake of shipping.

The origin of the name comes from Harry Potter fandom, in which fanfic writers shipping Hermione with characters other than her canon love interest, Ronald Weasley (or Ron), would often include some terribly contrived arc in which Ron goes insane from Hermione dumping him, and promptly joins the villains of the series, the Death Eaters, thus making it easier for readers to sympathise with Hermione's choice and hence the ship of choice.

Perfect, non-HP example of Ron the death eater in action:

In 2002, the second series of the Pokemon anime saw a cast change, in which one of the three main characters, Misty (who was heavily shipped with one of the other main characters, specifically Ash), was swapped for a younger model, May. Cue dozens of gratuitous rapefics written in May's dishonour. Voila: May the death eater.

Ron the death eater by WolfsBaneT9 January 3, 2013