I think if there were to be a book written of the most memorable entries on LJ in the past 10 years all the anti-(insert horrible pop/punk artist) communities cannot go without mention, especially one of the more active ones, anti_avril.
This community was fueled by a mutual distaste for the "punk artist", as the more "literate" music lovers of LJ found her get-up an insult to what punk represented. So, of course, the nature of the posts depicted proof of how fake she was, a ridiculous close-up, or whatever else was amusing in a negative light. It attracted plenty of people who all thought Avril was God or whatever. Needless to say, there was all sorts of interesting/amusing arguments. The community was compelling really! It was fun, and I met a lot of my LJ friends on there.
Unfortunately, eventually the posts became full of nonsense and the community maintainers shut it down, but the fans of it did open a new community, xantixavrilx
. It's definitely not as active, (probably because the spotlight has definitely shrank on the pop star) but it keeps the memory of the original community somewhat alive.