You can hone something (on a hone), or (if you are american 
) you can hone after something, but I am not aware you can hone “in on” something? “Homing missiles” are a real thing, on the other hand.
I’ve always said “home in on”.
“Hone in on” is the original expression on both sides of the pond (and it’s still in widespread use). But it’s not surprising people hear it as home in on and use that instead, because it also makes sense.
I think it’s the other way around.
If it makes you feel better, I saw them, thought “Huh, those bullet points look they’d expand if I clicked on them,” and then didn’t click on them, because obviously there was no way this message board software could have such arcane sorcery as collapsible bullet points.
A tale / joke my husband LOVES:
(Southern lady): Where are y’all from?
(Snooty northern lady): Where I’m from, we learn not to end a sentence with a preposition!
(Southern lady): Oh, I’m so terribly sorry to have offended, please let me try again. Where are y’all from, bitch?
The “where’s the broom at” is definitely not considered standard usage and would be expected from someone less educated.
Could of / should of is just plain wrong, and is a misspelling of the identical-sounding contraction “could’ve”.
Whom is the objective pronoun while who is the nominative.
You forgot split infinitives! You’re never supposed to put an adverb between the “to” and the “verb” e.g. “I’ve learned to walk carefully” vs “I’ve learned to carefully walk”. But there are times where it just sounds better to have it split, and I don’t recall it ever being a big deal in high school English class.
Let’s face it: languages evolve. Both based on common usage, and standardization of spelling, and so forth. Something that was Absolutely Correct a hundred year ago is not so today.
As far as phrases like “Straighten up” - to my mind. this is sort of a compound verb, rather than a verb followed by a preposition. I wouldn’t straighten down, or straighten over, or straighten on, but I would “straighten up”. I might lie down, but I wouldn’t lie up.
Oh - and lie vs lay - you forgot that one?? I was always taught that “lay” was something you did to something else - e.g. “Jane, please lay the fork on the table” versus “Jane, it’s past midnight, time for sleep, go lie down in bed”.
I thought about including it, but I’ve only met one proponent of not splitting infinitives in the past ten years or so. Figured it was a dead topic.
In high school, though, we had it pounded into us. Much like not using alright, the teachers kept drilling it in, but I kept seeing it in books, so the lessons never took.
ETA: I didn’t forget lie/lay. There’s not really much controversy over it, so it didn’t make my list. I do have a handy graphic (for the indicative) I made if anybody wants it.
We might add starting a sentence with a conjunction. Do you think that’s okay?
Most style guides are fine with it. My best guess is that the rule was really a house rule for schoolteachers to keep their students from starting every sentence with And. Not sure if kids are still being taught that today.
It seems to me that the subjunctive is still used in American English, but essentially gone in British. I had the following experience. A book I was coauthor of was being published in England. The British copy editor marked a dozen or more sentences of the general natural as the example “A necessary and sufficient condition that a functor have …” as wrong and should be replaced with has. Of course, we resisted, but I asked around and she was correct in British usage.
In my sentence above, I wrote without thinking about it, “A book I was coauthor of” and I consider that completely correct and will not change my usage. Often (but not in that instance) a “preposition” is really an adverb since it has no object. In fact, I consider the distinction between preposition and adverb to be the same as that between transitive and intransitive verbs. And just as many verbs can be used both transitively and intransitively, so many prepositions can also be used as adverbs. Consider the expression “Look up”.
And I consider the who/whom distinction a dead issue. It grates on my ear when people use “whom” incorrectly, but doesn’t bother me at all if people use “who” where “whom” would be formally correct. It is almost a tic with the Votemaster (whom I read daily) to use “whomever” when there is no transitive verb or preposition in sight. It seemed to be a conscious choice by Noam Chomsky to never use “whom”. Oh, and I don’t object to split infinitives.
And if not, why?
Chicago’s 16th edition offers this quote:
Chicago can be a little snarky sometimes. They do, though, go on to warn about using adversative or contrasting conjunctions (like but or yet) in a confusing way.
I think that sometimes, people carry descriptive grammar/punctuation/spelling too far. If “anything goes”, eventually there won’t be a mutually understandable language. Not everyone is a Twit, for example.
I haven’t seen mention of “myself” in place of “I” or “me”, as in “John, Joe and myself are all here.”
It grates on my nerves when I hear it.
ETA, I’m not calling anyone a twit, just pointing out that not everyone is aware of the latest Twitter jargon.
Also, “Our Strange Lingo” from 1902:
“Why English is So Hard”
Related:
“Phoney Phonetics”
Bonus:
Took me a minute. 
It’s not really a matter of anything goes, but there are a lot of things that are both widespread and at least perfunctorily accepted by some of the acknowledged authorities like style guides or dictionaries.
For instance, flaunt meaning “disregarded” has an entry in Merriam-Webster. Using your for you’re does not.
So we can discuss if and when the first might be right. There’s not much point in doing that for the second.
I seem to remember William Safire pronouncing “hone in on” to be okay because GHW Bush used it so often. I didn’t agree with his reasoning, any more than when he decided that “covert” (the adjective) properly rhymes with “overt”, merely because it was heard so often in the Iran-Contra hearings. Politicians don’t get to decide everything.
“On accident” sounds absurdly wrong to me, but if I hadn’t been hearing and saying “on purpose” all my life, I don’t think the preposition would make any more sense there. I’d suggest “by purpose”, or perhaps “with purpose”. Of course, preposition use changes. A couple of hundred years ago, you’d see “independent on” rather than “independent of”, and it does make more logical sense.
I’m okay with “alright”, because the two words are used synonymously. Imagine this dialogue–“Are you all right?” “No, but I’m about two thirds right”. You can’t, right? That’s why I’m okay with alright.
By the way, I usually spell “okay” “ok”, but I’ve tried to be more correct in this particular post. I reject “OK” because I don’t believe all-caps spellings of words of more than one letter can be right, and also I’m not talking about Oklahoma. “O.K.” is too much trouble for such a common word, and “okay” is ok but it looks too informal to me.
And then there’s “waiting for” vs. “waiting on”. I used “waiting for”, except when I’m referring to someone like a server. Is “waiting on” a regionalism?
“Home in” is the earlier usage, but they’re both very recent (comparatively speaking.)
“Home in” is first attested in print in 1944; “hone in” first in 1965.
Recent discussion here:
Here in Chicago, I hear both forms.