I believe fanfiction is an expression of affection of one to the canon it came from. You liking character B from show A for example. I don't give a snot about your self insert's spethulness, especially if I have to spend the next fifteen minutes trying to read bad chatspeak. (I learned English, and that is what I read). Fanfiction is a place where you can dwell on areas not fully explored in canon. And yes, to further yourself as a writer too.

When you say it's just fanfiction and:

1.) make the characters as OOC as you want to fill your story - you fail

2.) ignore basic grammar and spelling - you fail

3.) use chatspeak - YOU FAIL

4.) insert yourself in the fandom and display your fantasies to everyone on the net - you fail

5.) write a story so generic that you insert char A in this fandom, then replace with char B from that fandom to make a new story - you fail

6.) insert author's notes bigger than the story/or in the middle of the story - you fail

7.) don't even watch/read in the fandom but feel compulsion to display your writing based on random fanwork - you fail

8.) whore for reviews or you won't write more - you fail

9.) act like a spurned lover whenever someone leaves you less than sparkling praise, flame them on your page, then proceed to hunt them down and revenge flame their stories - massive fail

Someone posted this and I thought it explained something quite beautifully.

Ebert's Law

When you ask somebody to try their own hand at something before criticizing your efforts, you have violated Ebert's Law and lost the argument. Roger Ebert is not a filmmaker, but he knows what he likes and doesn't, and has every right to say so. Similarly, people don't need to be chefs to recognize a good restaurant, or musicians to appreciate a symphony.

Person 1: Your story is rubbish!
Person 2: I bet you couldn't do better!

Person 2 has violated Ebert's Law