For me, any black metal band that backed off their original image lost it for me. Not that I ever really cared for those bands that just tried to be as gruesome as possible. The example I'm thinking of is Satyricon. The video for Mother North pretty much introduced me to black metal and then Satyr goes and cuts his hair and tries to look like some greaser from the 50's.

Sorry to be predictable and typical, but, Mortiis. What used to be some kind of bizarre alter-ego slowly turned into little more than a mask, which one day he just ripped off on stage. He also ruined his hair by turning them into dreadlocks; during the 90s he had particularly nice, long black hair.

^^Yes. His early cryptic dungeon goblin image was obviously silly, but it suited the music and helped create a certain aura around him. Once he started featuring in Kerrang in limos sometime in the late 90's, it totally killed his mystique and he became a complete joke.