But that's the thing that rubs me raw about everyone tossing around Mary Sue (or Marty Stu) willy-nilly -- whose Mary Sue are they? They're long-established characters that have been around for longer than many new players have. They were established by some writer, somewhere, some-when, and then changed, and used again, and changed, and used again, and again, by different writers each time, heck sometimes by different companies each time.
They're not some fanfic insert, any more than Captain America or Superman are (zomg so noble and powerful!).
They're characters some folks don't like, sure, and I have no problem with that. I just dislike the term being thrown around wildly, when all people really should say is "that's a character I don't like." As it is, the term gets used so much it's losing all meaning.