The intricacies and controversies involved in creating back-of-the-book indexes.
Me too, for both the topic and the practice.
I first saw this as “alcoholic volkswagens”. That would be an interesting topic.
Driverless car concepts.
How the NFL and NCAA are evil, even though I enjoy watching the games.
A topic?
Everything I know anything about, and a whole host of things I don’t know squat about. It’s just my way.
Investing
Sherlock
Restaurants
The Big Bang Theory
Jane Austen
William Makepeace Thackeray
My latest big bargain at a thrift store
Genealogy
the book of Genesis
my job
Everything I find interesting, apparently. 
Me too. It’s why I don’t talk to people about my hobbies very much.
Nietzsche. Existentialism in general.
The ill effects of the car culture in the United States.
That’s the only thing. Really, I’m usually much more of a listener than a talker. But the stupid car culture in the US seems so clearly applicable to so many things, and no one ever talks about it, so that’s one area where I go on rants and inevitably bore people.
“Why are Americans so fat?” Because of the car culture. No one walks anywhere anymore.
“Why can’t we have a reasonable drinking age?” Because you have to drive everywhere in this country. In France, drunk 18-year olds can stumble home from the bar or fall asleep on the train.
“What’s up with all this social isolation?” Car culture.
“What happened to our pretty historic downtowns?” Car culture.
“Environment?” Cars.
“Dependence on Middle East oil?” Cars.
And so on.* But see? I’ve bored you already!
*Yes, I’m overstating the case on many of these points. But I do think the evisceration of American public transportation and the almost exclusive reliance on cars has had all sorts of bad effects on American society.
Electronics; specifically, what I make, although I don’t actually talk about it much unless somebody else brings it up, as in “What do you like to do?”.
After being serially conversationally victimized by my ex about Magic the Gathering cards, I no longer bring up my hobbies/pet topics unasked (and don’t drone on about them). But, if I let myself, I could talk all day about:
[ul]
[li]marching band/drum corp shows[/li][li]online gaming in general, WoW in particular[/li][li]white privilege[/li][li]the death penalty[/li][li]equal rights wrt gender/sexual orientation[/li][/ul]
Ferrets
My sailing trip
Relationship woes
The corollary is that somewhere in the world there is a person who can bore you to death on the same topic.
Most recently? Mass Effect, but Babylon 5 or Star Trek are both longtime classic for this as well.
Also, aviation trivia. I live on an airbase full of people who don’t want to talk about airplanes.
Failed American gun designs
I think you win.
Sherlock Holmes
Fountain pens
Neither of those take long.
Dressage and how adorable/clever/special my cat and horses are.
For those of you who don’t know, in spite of the Olympics and all the hype about Ann Romney’s horse, dressage is French for “training” and refers to a style of classical horsemanship that requires strength, balance, focus, passion, and athleticism in both horse and rider. See, I’ve already lost some of you . . .
I think the topic that we can all bore each other to death with is dreams. Paradoxical how something so magical and engaging turns to ashes once you try and talk about it.
‘Let me tell you about this amazing dream I had last night’ is reliably followed by a really boring, one-sided passage of conversation.