Generally, I’m not in favor of having a screaming hissy fit over borrowing of OC’s without permission in cases where it seems like the borrower just hasn’t been around fanfic enough to realize the social codes. If they in turn throw a fit and refuse to change when asked by the character’s originator, that’s a different story. The finer points of etiquette in a fanfiction writing community can seem contradictory. We borrow from officially released material and characters all the time, but the use of specific events and characters from others’ fanfiction is frowned on unless done with specific permission. Without taking a deeper look at things, it can seem a little backwards. The reasons why I see the current status quo as the right way of doing things are as follows: 1) Licensed material is available for checking and that makes it impossible for a writer to be able to pass a character/idea off as totally their own. People have read the books and can check Wikipedia. Thus the official books, movies, etc. are considered fair game for fanfic inspiration. Fanfiction is unofficial and can appear anywhere on the Internet. It’s more likely for a fanfiction plagiarist to get away ganking an OC or other specific piece of the story. 2) Original characters and other unique features of a fanfiction can be very personal. Having them show up somewhere else without warning crosses a line for most writers, for any number of reasons. I think the social faux pas associated with non-approved use of OC’s is pretty strongly influenced by this discomfort. There is also the possibility that the use of said characters might be conflicting with the author’s beliefs/intrusive and annoying (you should have done this instead and this is why!)/disturbing/whatever. Fanfiction is in some ways a small town and in others a big urban city, and the sense of having proper boundaries is important to maintaining a good community atmosphere. 3) Some writers seem to believe that others’ use of their plots or characters will somehow ruin the original or make a different ending than they had planned the “real” one. I don’t really get this, but it seems to be a very common reaction and I see it a lot in writings by pro writers who have banned fanfiction of their works. In these cases, I think it is best to be kind and polite: don’t use whatever they don’t want used in your stories. Everyone has their own quirks, and many perfectly lovely people just have a strong negative reaction to the idea of someone messing around in their sandbox, even if it’s entirely unofficial. I think that is a feeling worth respecting. Plots can and do turn out creepily similar without any ill-meaning on the part of the next writer. Sometimes I’ll avoid reading stories that I think are going to go down too similar of a path to something I’m working on. Others times I tell myself “stop being silly” and read it anyway. It can be a tricky area, but generally I fall on the side of using the similar elements anyway and just making sure to keep it different enough.