I don't write much fanfiction anymore. I am trying to get a published writing career going. But It can be just as tough to create your own characters for your own universe and have them not labelled Mary sue. Many of my friends don't understand there's a fine line between between 'write what you know and have experienced' and Mary Sueness.

so it isn't just in fanfic. I even have a friend that unless the story is male/male slash, her Mary Sue radar goes overboard.

I want to say one other thing: there's a fine line between an intelligent, well-created self-insertion character and a Mary sue. People don't get it, nor do they seem to get that canon characters can be MS-by-proxy, also known as 'placeholder characters'.