Cast iron frying pans. Whether or not there is any other form of pan that one should consent to own and actually attempt to cook food in. How to season them properly. Whether it is a mortal sin or merely a venal sin to ever wash them. What kinds of spatulas or spoons are to be permitted to come into contact with the food therein.
Ahunter3, happy owner of 2 standard and one ultra-deepdish 12", two 10", and two 6 1/2" cast iron frying pans.
Liquid drain cleaners (Liquid Plumber, Drano, etc)
Recumbent bicycles vs. road bikes
The quality of Robert A. Heinlein’s works, particularly his later works.
Guaranteed to start a fight. Kind of esoteric, but bound got get ugly fast.
The tinfoil hat skirmishes on the fringes are quite gory.
(The unknown threatens this board so much that they react like good cavemen and try to kill it.)
Which diets “work” best, in particular the Atkins diet and carbohydrates. That one specifically has set off several threads that went up in flames.
Whether it’s okay to give your child a made up, or creatively spelled name.
This teaches us something.
The more obscure, esoteric, or technical the subject, the more vicious the knife fight.
True or false?
Whether it is ever justified or appropriate to use some kind of stereotype or take notice of a pattern when referring to the sorts of news stories that come out of a particular state.
The typical post goes “blah blah blah, news story, link, blah blah blah blah, cursing, more blah, more cursing, and of course it happened in Texas, huh? ;)”
The Texas crack is a small part at the end of the post, but pretty soon someone will come along and say the usual about painting with an overly broad brush, and then another person will come along with a rejoinder about how even if not all Texans are ___ it does seem that we’ve seen a lot of stories about ___ out of Texas lately, so is it really unfair to deny the pattern?
From there it just gets nasty. Happens with other Southern states, too, but don’t we always see these kinds of flamewars about Texas? 
Similarly: barbecue. The only thing BBQ fans agree on is that their kind is the only kind.
Kids on airplanes.
Anyone remember the fight about drier lint?
Have seen this happen only once, but it was quite vehement: whether diabetics should inject themselves at the table while dining out.
WRS
You phrased the question wrong. Should be “Is Cecil many real people?”
Heretic! Blasphemer!
And so on.
WRS - 
The truth will set you free, even if it’s not quite pleasant.
Ditto Starbucks plus the added advantage of the “is their coffee any good” angle.
Discussions of “2001 A Space Odyssey”?
Decisions hang for ages on either blindingly brilliant or blindingly bad.
Witness the current thread on Cafe Society.
and
That thread is as civil as any you’re likely to see on this message board. It’s just a bunch of people discussing an article about the series, some of whom think the author’s criticisms of Star Trek are misplaced, others of whom think that he makes some relevant point. A few people have expressed some disdain for the article’s author, but there’s no venom at all in the thread, no abuse being hurled back and forth. Hell, i couldn’t even find a swear word.
Oh, sure it’s civil, as those Dopers who disagree are directing their attacks to Card himself and somewhat respectful of his status as a published SF author. Now imagine the firestorm if Card were a Doper and had posted his article in Cafe Society. At best, he’d have been accused of living under a bridge. At worst, it would probably result in one of the more fascinating meltdowns in the history of the SDMB.
Just remembered another one: telemarketers.