No offense meant to anyone who writes or likes such things, of course. I dislike the story, not the author or readers. :)

• Original characters: in original fiction, these characters are perfectly acceptable, but I prefer reading about canon characters when I read fan-fiction. Why else would I read fan-fiction if I wasn't a fan of the characters?
• Mary Sues: whether an original character or a "canon Sue", I dislike their too-good-to-be-true features and their interruptions of existing structures within the story universe.
• Heterosexual romance or sex: a very personal preference, but one that is strongest with fan-fiction. I'm not heterosexual and I find heterosexual relationships unpleasant to read. I do read published romantic suspense novels, which are usually okay.
• Real person: this strikes me as invasive and unnecessary, since I'm a fan of characters, not the actors portraying them - because I know nothing about those actors. Therefore, I won't read this.