Fanon is great, to an extent: the problems come in when you get fanon based on fanon based on fanon etc. For example, Alice was originally cold and antisocial, and fans used that to turn her into a tsundere. A bit far from her original personality, but still okay. However, then some fans emphasized the dere part until she eventually turned into a moeblob. New fans often think canon Alice acts like her depiction in Marisa Stole the Precious Thing, when that's almost the opposite. The same can be said for altering the character designs: there have undoubtedly been times when a character was drawn so differently from the official designs that you would never know who it was if the artist didn't say.

On a more personal level for me, I accept that Tenshi could be a masochist, but it's annoying how she's been reduced to a drooling slut whose sole purpose in life is to get people to beat her up.

Pad was NEVER funny.
Ran and Yuyuko are practically retarded.
Shiki is a midget.
I'm upset.

>>157
To reference IOSYS for a second time, I would like to draw attention to their interpretation of Shikieiki, which they made out to be a vengeful bitch, rather than the caring girl she is shown to be in PoFV. The character took a complete 180, and has been used as reference for many fanworks, which ultimately ruined the enjoyment of fan work containing Shikieiki for me.