I was also taught “no space between number and units for SI units” (so 50Ω would be correct), although looking stuff up that does not seem to be the universal standard.
Maybe it was so that old word processors would not split the number and unit over a line break (in the days before non-breaking space was a thing).
It may have been simply to save space and make typesetting easier back when that was a thing.
The AP Style Guide is mostly geared with that in mind. Which is different from something like (say) the Chicago Style Manual.
The first two are reasonable, if very often not followed. The second just looks odd to me, the difference being the presence of that degree sign which acts as a separator. This is probably why I’ve never seen any official weather reports in either the US or Canada ever put a space in there.
To me this makes absolutely no sense. How would you say “23°C” in words? The standard form is “23 degrees Celsius”. “Degrees” is logically associated with the number; the “Celsius” is just the units qualifier. Or to put it another way, it’s much more closely bound to the number than to the unit; the number specifies “how many degrees” there are, the “Celsius” just defines the unit.
Then they’re doing it wrong. 
As mentioned by Dr. Strangelove, NIST should probably be considered the final authority on the matter. NIST Special Publication 811, Guide for the Use of the International System of Units (SI), is sorta the bible for this stuff. And it says, “There is a space between the numerical value and unit symbol, even when the value is used as an adjective, except in the case of superscript units for plane angle.”
The same way you do. I fail to see how “(23 degrees) Celsius” is any different from “23 (degrees Celsius)” in this respect.
Regardless, the important practical point is that C means Coulomb. You need to write °C if you meant Celsius.
Exactly. The symbol for the unit is °C, not C.
The only time I become pedantic is to turn the tables on an annoying pedant. I also love when it fails as when Jerry points out that a whale is a mammal in one of the funniest sitcom bits of all time.
NIST is the final authority on weights and measures and related technical matters. What we’re talking about here is punctuation, which like all matters of orthography is an arbitrary matter of style (and common sense) that’s determined by common usage, such as the consistent usage by national weather services. NIST has no special authority here (and neither does their international counterpart) and there’s no such thing as “wrong”. There is, however, such a thing as “odd, because very few actually use it that way”.
So if I write “it’s going to hit 32C this afternoon”, you would think that there’s somehow going to be a big electric charge buildup somewhere equal to 32 coulombs? 
I’ll nevertheless concede the point about where to put the space if you’re going to insert a space, but absolutely will insist that no space is needed when describing temperatures, that the form “23°C” is the one most commonly seen and therefore the de facto standard, and that writing “23C” on a message board by someone who can’t be bothered with the degree sign is perfectly acceptable, too.
See, I’m only a part-time prescriptivist! 
I would always write “23 C” on a message board or casual email, but if you’re going to be pedantic, you should go all the way. And that means going to NIST.
In my experience, it’s rare to even see these abbreviations outside of scientific publications. Weather reports just say “70 degrees”. You don’t even get the unit.
We all have various things that bug us. But when you say, “the easiest way” is to open up something I’ve never used and would have to spend some time to find, it strikes me as much easier to simply type 30 C and realize that everyone who reads it is going to understand what I wrote, with only you and a few other being annoyed.
Anyone read that book about the 2 guys who crossed the country correcting misspellings and grammatical errors they encountered on signs? It culminated with their being arrested for something like adding or removing a comma on a sign at the Grand Canyon - that was designated part of a national landmark. An enjoying read about a couple of pedants who put their annoyance into action!
It depends. Check out the National Weather Service. For a weather and forecast summary for any given area, they give the temperatures in degrees Fahrenheit (with no space). Same with Environment Canada. However, this tends to be the case for the graphic summaries. For EC, if you scroll down to the detailed forecasts in words, they not only omit the unit, they omit “degrees”, too. So you’ll see something like “clearing tomorrow with a high of 12. Wind northeast 15 km/h gusting to 30.”
Except apparently @Dr.Strangelove who will understand it to mean 30 coulombs.
thats dogwhistle for “not from an old black guy who plays the guitar”
edit to add:
/s
I think the list of the ways I am not annoyingly pedantic would be shorter.
I don’t know if it’s exactly pedantic, but it’s certainly annoying: when people ask things like “anyone have any questions?” or “is everyone doing ok?” I have a tendency to answer “I don’t know”.
(Three logicians walk into a bar…)
Is this the place to confess that I’m starting to leave the period off of common abbreviations, especially for various street type names: St, Dr, Ave, etc.?
It started with fretting over whether to use two periods when a sentence ended with an abbreviation. I write a lot about streets in emails.
And if you’re writing Dr for Drive, why not Dr for Doctor?
Despite what I sometimes hear, you do not need to notate the file.
Note. It’s just note. You “note” the file.
The other day, I had somebody tell me that they had a chance to “conversate” with someone.
You mean converse?
Oh, and baseball players score runs. Not points. I remember going to a baseball camp when I was a kid, and it drove me nuts when the head of the camp (some guy named Chet Lemon*) joined a game and kept talking about scoring points to catch up.
*sure, he was an all star center fielder for the Detroit Tigers. Sure, he won a World Series. But points?
Duly noted.
As a software developer, I have a bunch of things to be annoyingly pedantic about, but code style is my worst.
Writing code is a group project, and unless we agree to a specific style - to which I would adhere - it becomes very hard to merge differences when, say I write some code in a file, and someone else does with a different style.
I know it is a niche annoyance, but it is a real one I face every day.
I’m going to be pedantic about something from the first episode of the new season of Star Trek: Discovery. The characters kept calling rocks falling from the side of a cliff an “avalanche”. “Avalanche” means snow sliding down the side of a mountain. What they were experiencing was a rock slide.
… for the record …
I am NOT pedantic, I am just right!