In the field of linguistics, there are two basic approaches to defining the rules and grammar of a language: prescriptive and descriptive.
Prescriptivism is a school of thought guided by the idea that there should be a correct way to use words, and we should teach people those rules so they stop screwing up and perverting the language. Descriptivism, on the other hand, says that there is no "correct" way that any language should be used, there are only the various ways that language is used, and as time goes on, those uses naturally shift and change.
According to a descriptivist, you can observe, for example, where English speakers tend to place prepositions—up, down, here, there, etc.—in relation to other parts of a clause, and you can describe any "rules" you're able to work out. But if, 30 years later, people are no longer using prepositions in the same way, that's not a perversion of English, that's just the natural, inevitable way that human language changes over time. People aren't breaking the rules. The rules have just changed.
But prescriptivism says that (I shouldn't have started this sentence with "but," and also) you should never put a preposition at the end of a clause. If you do so, you're just wrong, but also dumb, and bad, and destroying the English language. One classic story from history has Winston Churchill responding to an editor who zealously tried to enforce this rule by labeling it "the type of errant pedantry up with which I will not put."
Of course that never actually happened... and it's really only funny(ish) if you're at least a bit of a grammar snob. But it does illustrate a couple important points:
First of all, being a grammar snob has very little to do with being smart. Thanks to the advent of the Internet and services like Grammarly, a smart person can easily achieve flawless academic/professional grammar without wasting energy on snobbery. And the second point the story makes clear—since the audience for the joke is the same group being mocked—is that most grammar snobs kind of hate themselves.
There's Nothing Wrong With Saying "10 Items or Less": Descriptivism vs Prescriptivismwww.youtube.com
And with good reason. As any grammar snob worth their salt will tell you, prescriptivism has been pretty much abandoned by linguists. It is purely the realm of "errant pedantry." Any means you use to communicate can be valid, as long as you effectively get across your point. And yet...every time I hear someone use the word "irregardless" I flinch.
When someone near me says they "could care less" or "God only knows" or "that's a whole nother thing," I have to actively suppress the urge to blurt out "couldn't care less," "only God knows," and "it's an other, not a nother, you can't just start splitting up words wherever you want! You can't take a 'bat' in your 'htub', Steve!" And don't get me started on "literally," or I will figuratively explode.
Needless to say, this energy is neither healthy nor useful. The only advantage being a grammar nerd provides is that you can usually avoid being judged too harshly by other grammar nerds. It's a relic of old class hierarchies; a shibboleth indicating membership in an exclusive club that fewer and fewer people still care about—and that even a lot of the membership thinks should be abolished.
So why do we hold onto these fixations? Why don't we just stop being grammar nerds? The short answer is that we can't. There's an evil little voice in our heads that screeches when tenses become confused or subjects are made to disagree with verbs, and we just want everyone to stop upsetting the voice.
The slightly longer answer is, we were indoctrinated into a value system that encouraged us to apply inordinate attention to the words we use, and we resent people who have a more casual relationship with language. At some point someone made us feel bad about speaking "incorrectly," and we hold onto some of that insecurity. Even if we know better now, some part of us prefers to interpret a lack of interest in speaking "correctly" to laziness, inattention, or stupidity—rather than freedom from our weird hang-ups.
It's like there's an elaborate obstacle course that a handful of us are desperately trying to navigate while everyone else just ignores the cones, ducks under the hurdles, and walk around the climbing wall. While the devotees are still jumping through pointless hoops, the non-weirdos have already gotten where they're going. And while their methods may offend the clique of obstacle course-nerds, there's no denying that they get across the room with a lot less stress and effort.
So please, the next time someone says to you, "I don't know, can you use the bathroom" or "I think you mean 'fewer'", just have pity on them, nod politely, then go back to just—you know—talking normal, however. Who cares, even?