Similarly, if someone only knew about The Beatles from SDMB, they would think that A Day in the Life was the Beatles’ best known and most liked song.
In every thread about books, someone will eventually drag it into a dull and nitpicky discussion about Lord of the Rings.
Maybe more IRL than online, but…
Every time someone describes a chocolate dessert, it is either “to die for” or “decadent”.
Every time someone describes tasty ribs, they are “fall off the bone”.
mmm
Every time there is a pet thread, someone will neglect to attach photos of their pet
Recent example, every time someone mentions checking luggage for a flight someone will chime in, “Checked bags? I can put everything I own in my carry on.”
So true.
In every thread where somebody posts a request for technical support, the OP never posts again. No replies with requested clarification, no acknowledgement that something fixed the problem.
Even worse are the ones where the OP does post a response that is just “working now” with no indication of how the problem was actually fixed.
(Obviously “every” is an exaggeration, but I’m sure we’ve all searched on some problem we’re having, found a post someplace of somebody else with that exact same problem, and no further participation from its OP to help arrive at a solution.)
As a corollary, maybe not so much here, but on computer related boards in any thread where someone asks for help with Windows, someone will say “install Linux”.
Not just on the Dope . . .
When a thread has Facebook in the title, in my head I set the under/over on how many posts it will be before someone declares they don’t use Facebook.
Oh please don’t! I can feign ignorance about Windows or Mac, but I’m the Linux guy. I probably know the answer or can figure it out.
(First time upon meeting an ex’s Dad, after a cross country road trip, he immediately recruited me into helping him get XFree86 working.)
In every thread about bad song lyrics, someone will cite - with tremendous cleverness and insight - “MacArthur Park” and “A Horse with No Name”.
mmm
Hey, is the Constitution a suicide pact?
I any discussion about DeLoreans, someone will mention flux capacitors or 1.21 gigawatts. I know this because one came up on Barn Finds recently. Some people in the comments were discussing converting them to electric, since the engines in these were such crap to begin with, and I had the impulse to to ask how they would generate the 1.21 gigawatts needed to power the flux capacitor. But I stopped to think first and didn’t post it, because I didn’t want to be “that guy”.
I once was had as a greenhorn student in electrical engineering in my freshman year in 1989. Some of us discussed a circuit problem, and a fellow student casually declared “You need a flux capacitor to do that”. So two or three of us (including me) answered “Interesting. What is a flux capacitor?” (we already had learned about multi-vibrators and flip-flops, so why not?). He only asked backed “Have you ever watched ‘Back To The Future’?” 
You just were.
You just were.
In every thread about religion, someone always starts an argument of what atheism is.
And almost all of these threads go downhill from there.
Strike out that last sentence’s “almost”.
Definitely! Atheists are terrible the way they complain when other people tell them what atheists do and don’t believe.
Oh contraire: It gets really hot when several self-professed atheists get into an argument.