Oh, gosh, there are so many that I remember and that have affected me. There was one, though, that upset me so badly and made me so upset that I quit reading fanfic for at least a year. I won't put the name here in deference to the author, but it is a fic that is very often talked about. Maybe it was just my state of mind at the time, and I keep thinking I'm going to give it another try, but I don't know if I can because the memories are so painful. I did email the author and told them how extremely sad that I thought it was. (The person doesn't know I quit reading fanfic for awhile because of it, though.)
Nancy