There is a law, which may or may not be named, which goes thusly: there's a rant or a story or a meta that you will eventually post somewhere, and it will be something you don't necessarily feel in the morning (or maybe you will) but it will almost certainly not be something you put every possible effort into, just something that you shot off because you were on fire or annoyed or inspired.  Just one post.  And it has your handle on it, and it will follow you until the end of time.

For me, that's the Mary Sue Litmus Test.  End.  Of.  Time.

For you, it could be a meta on the Sam/Dean relationship, or a poem you wrote about Rodney McKay, or a pissed-off reply to someone about basic human rights, or a scathing critique of the body odor of the showrunner of your favorite series.  Could be an essay or series of essays on fandom, for random example.  You won't know, not until it's out there and suddenly everyone on the planet is linking to it for a week.  Or a month.  Or more.

You wrote something.  And it's been linked.  Maybe it's been linked by someone doing a dissertation on slash as the modern face of online feminism.  It could just be put on a list of stories enjoyed by misogynistic jerks.  May all that's holy help you if it gets quoted in the mainstream media.  (Dr. Merlin has long had a ticklish relationship with the BBC.  Frickin' Harry Potter making fanfic trendy ever year or so.)  But it's out there, in a place where you never expected to find it, and you kinda wish the people there hadn't found it either, not least because you have this sinking feeling the next person who reads the post is going to be your mom and when she finds all the gay porn you've been writing, holiday dinners are just going to be even more awkward than usual this year.

So, little fanthing, what do you do?

Well, first off, realize that absolutely anything you put on the Internet, no matter how well locked and filtered, can be made public, either by accident or by design of someone who doesn't like you as much as you thought.  That includes email.  That includes things you've marked "Private."  No software is 100% secure, and every password can be hacked by someone with enough interest.  If you put it out there, anywhere, assume it is not safe.  If you post a screed about how Fangirl X is such a raging bitch, there's a chance she'll see it.  You may just be venting, you may not even really mean it once you've said it (or you might), but it's out there.  She'll find out.  Meanwhile, someone will make a screengrab of your flail over the latest casting kerfuffle.  Someone else will quote you out of context to support their personal agenda on the neverending het vs slash vs gen vs femslash vs pie debate.  Someone will find those naked pictures.  Own your words, or don't say them in the first place.

Second, for the love of Bob, use a pseud online.  That doesn't mean you should go around sockpuppeting.  Pick one (or two if one's your porn-writing handle) and stick with it.  Make it yours.  When you log onto a new forum and someone asks, "Are you the same UsernameOMGsquee from Previous Fandom?" and you are, say yes.  Don't link it to your real name.  Back in the day of oh ye gods we were young, a lot of fans got their access from schools and had to use their real name-linked school accounts.  You live in the age of Gmail.  Embrace it.  Plus, unless you hand out the URL of your fannish website in your resume, it's going to be very hard for a potential employer to associate UsernameOMGsquee with Susan Q. Fangirl.  This will come in handy later.  Yes, even if you're a writing major.  Especially if you ever want to be published in the big leagues.  Separate your online handle and your real life now, spare yourself the pain of Mother asking, "So dear, where did you learn about different brands of lubricants?"  (This might not be a problem for you.  Mother Merlin used to help judge fanfic awards in Forever Knight fandom.  Father Merlin wrote genderswap.  Longhand.  NOT FAR FROM THE TREE, PEOPLE.  NOT FAR AT ALL.  A friend recently posited the existence of a "fandom gene," and she's probably right.)

Third, ask.  People are sometimes just misinformed and don't realize you have no interest in the publicity.  If you say "Don't quote me, don't use that, don't link to that page," and explain it's a privacy thing, as often as not, they'll say sorry and cut it.  If you're polite about it, so much the better.  (I know, I know.  The Tone Argument.  I'm just sayin' that "Please remove that link as my dear old grandmother will have a stroke if she sees it," may yield a faster result than "Strike me from your records, you jerk."  YMMV, and your anger may be greater.)

Fourth, some people are assholes and won't say sorry or cut it, which is how the fannish identity of a New York Times best-selling author kept getting outed on a fansite which will not be named because we're not sending them traffic.  You can't cure stupid and you can't cure assholishness, so please refer to point one.  If you said it on the Internet, especially if it's embarrassing, or can be twisted to suit someone else's purposes, the probability approaches 100% that it'll get grabbed, quoted and used by someone you'd like to dip in sauce and throw to the fire ants.

And now, here's the reverse of that coin: don't be an asshole, and don't, when possible, be stupid.  Many people are happy to see their work recced and noted and acclaimed far and wide, and many people are not, and the best way to figure out if the person you're citing for your thesis wants zir fannish identity out there is to ask first.  Begging forgiveness rather than permission is an old trick, but fans talk to each other, and there's nothing we shout out faster or louder than the names of people who break the rules and screw over (intentionally or not) their fellow fans.  Recs tend to be okay, because they stay among our peers.  The second you stray outside fannish circles, be it for a paper or an article, you'd better ask.  (This is why Firefox News has discontinued our fanwork recs.  We still consider ourselves more a fannish space than a news site, or at least Dr. Merlin does, but we get picked up by bigger feeds and would like not to bring down the Wrath upon our fellow fans.)

Don't use the words of other fans to hold up your cause without making sure they're okay with it, and sure as hell, don't ever show those words to the stars or send them to the production team.  No, really.  NO, REALLY.  What happens in fandom stays in fandom, and freaking out the talent with kinkfics or badly-edited screeds or lists of reasons you hate particular characters is not going to help your case among the rest of us who then have to live with your misdeeds.  In fact, it's going to make us look at you with anger, disdain, familiar annoyance ("What?  Not this shit again.") and yet again new attempts to point out that we're not all illiterate misogynistic racist homophobic jerkholes just because we are also fans of XYZ.

Shorter: before you do something, think about how much you're going to make the rest of us look bad.  Then alter the behavior.  Making yourself look like a dork is part of being online in fandom long enough.  Making your friends look like dorks with you will make them resent it and you for freaking ever.  Trust me on this.