If you ever happen to wander into a Jane Austen fan community, never, ever mention Fanny Price. However polite and proper and old ladylike you might think Austen fans are, they can get as crazy as anyone else when the subject of her comes up.
And whatever you do, don't bring up the ITV specials. Especially "Mansfield Park".
It's also prudent not to state strong opinions about Marianne Dashwood, particularly if you have thoughts on whether she should have ended up with Willoughby or Colonel Brandon.
The next time you find yourself in a situation that necessitates causing a punch-up at a fantasy convention, go into a crowded room and yell "The Balrog has (no) wings!" Some fatalities are likely.
Even people who agree about Balrog wings or the lack thereof can sometimes find themselves at each other's throats over the issue of whether or not Balrogs can fly.
The flame wars over the merits of the works of Robert A. Heinlein have been raging since before the World Wide Web was invented.
Here's a neat trick. Walk into a Les Misérables forum and throw a metaphorical dart. 75% percent of the time you'll hit one of the following arguments: Cosette vs. Eponine, Frances Ruffelle vs. Lea Salonga, or Michael Maguire vs. Anthony Warlow.
Say how much Harry Potter sucks to Twilight. You'll get 3rd degree burns.
Ginny, just plain and simple. Bring her up and you'll hear that she and Harry belonged together, or that she's just a fan girl who doesn't love the real Harry Potter.
Same for Ron. Hermione too.
Wonder whether or not Ginny is a slut for having three boyfriends in two years and kissing one of them in a deserted corridor. It will not be pretty.
Dumbledore, a manipulative bastard or not?
Bonus points for using "the Dursleys," "Severus Snape" and "Tom Riddle" all in one sentence.
Never, ever EVER EVER say Neville Longbottom or Luna Lovegood are anything less than uberamazingawesome. God help you if you outright don't like them.
Say the movies are better than the books and that the first two films were too long and faithful. Declare that Steve Kloves and/or Alfonso Cuarón are brilliant.
There's a whole artform of not saying either "Philosopher's Stone" or "Sorcerer's Stone" because they'll both start Flame Wars full of Misplaced Nationalism. The first installment of the series must always be referred to as "the first book" or "the first movie". If it's already well-established that you're talking about Harry Potter installments, it can be innocently abbreviated as "Stone". If you have to refer to the object, say "the stone of the title" or "the titular stone". It's the only way, my friend.
Similar to the Twilight effect, mentioning R.A. Salvatore's Drizzt series on just about any Forgotten Realms forum is going to set the forum on fire, haters and lovers will clash over and over again, even the seasoned forum-goers seem to ignore the obvious flamebait.
A Song of Ice and Fire: "Hey, what's Martin's deal? It's been years since A Feast for Crows. When is he going to write this book? Is he lazy? Does he hate fans?" Oh, the flames. The flames.
Also, expressing any strong opinion regarding Catelyn Stark is generally like to spark a flame war between those who see her as a truly tragic woobie and those who think she is a self-pitying moron.
Mention Twilightanywhere on the internet. Just mention it, and watch as fans and anti-fans tear themselves apart over it.
Among fans, any character interpretation, any ship, any scene, ANY DETAIL. There will be a strong enough anti-anything faction to start a good-sized war. Most common: Edward's abusive, Jacob's forced kiss was in no way sexual harrassment, Bella's the most anti-feminist character ever... and you can't mention Breaking Dawn in any capacity without starting some shit.
The Wheel of Time series also kicks these off regularly, with backdrafts being caused by fans arguing over which is the best book or character, or by someone innocently asking who killed a minor character in Book 5 (an unimportant mystery that has nevertheless probably generated more discussion than the rest of the series put together), or if Jordan deliberately doubled the length of the series to make money or if it was instead a valid artistic decision. Probably the most devastating backdrafts can be caused by claiming that the male-female relationships in the books can be construed as unhealthy, juvenile, unrealistic, not particularly funny or somewhat sexist, which can generate counter-arguments from some fans of epic proportions. The choice of writer to finish the series after Jordan's death also generated considerable heat.
Anywhere on the Internet, make a topic about Ayn Rand. Positive or negative. Doesn't matter. The sheer volume of Fan Dumb and Hate Dumb guarantees a nice flamewar.
Mention the Gor series...well...anywhere. Bring popcorn.
In-universe example: in the short story "Wikihistory", by Desmond Warzel, time-traveler forum poster "SaucyAussie" seems concerned that discussion of certain sensitive historical events carries the risk of Internet Backdraft:
At 17:12:52, SaucyAussie wrote:
AsianAvenger, you're not rehashing that whole Nagasaki issue again, are you? We just got everyone calmed down from last time.
Similar to the Theater example, go ahead and bring up Gelphie or Fiyerba in any Wicked forum. For the most part the fandom is fairly polite about it's shipping (and both of them are technically canon) but brought up in the wrong space it can get...ugly.
Things can get ugly in some Animorphs forums if you mention actually liking Cassie.
Treat yourself to a crate of wine/beer/other drink of choice. Make sure you have plenty of food to hand, preferably ready-cooked. Then go to a His Dark Materials forum and suggest that Will and Lyra actually had sex (or didn't). Watch the fun run and run!
