Is the word "majorly" now a valid descriptive word for everyday conversation?

In My Humble Opinion
1

As in “majorly upset” etc. as a substitute for “quite” or “very”? Is this now an grammatically acceptable phrase in everyday conversation and written communication?

2

Define “now.” According to the OED, it’s been used that way since at least 1983, and the word “majorly” dates from 1955.

And certainly it’s grammatically acceptable. What rule of grammar does it break?

3

The Strunk & White grammarian rule of annoying the hell out of older ears.

4

Word

5

I’ll put my curmudgeon credentials up against anyone’s, and it doesn’t bother me – I’ll use it myself in conversation, though I certainly wouldn’t in any but the most casual writing.

6

Admittedly, it is what S&W would certainly call an awkward adverb. But they merely say you should avoid constructing it, not that constructing it is wrong. And remember, the book is “The Elements of Style,” not “The Elements of Grammar.”

Further, “annoying the hell out of older ears” is hardly a fault, since, if followed, it would have stopped words like “bus” or “mob.”

7

I fear that I might be hijacking this thread, but I’d like to know if this could be considered a grammar mistake. Essentially, people who use “majorly” are adding “ly” to an adjective to make an adverb in a novel way. I wonder if that could be considered a grammar mistake, if you believe in prescriptive grammar. If I coined a new word, “fastly”, to be to adverbial form of “fast” (instead of quickly), would I be grammatically incorrect if I said, “I went to the store fastly”?
Furthermore, what if they had declined to add the “ly” suffix, and just used “major” as an adverb? “It was a major dumb thing to do.” If that’s grammatically incorrect, then why would simply adding an “ly” make it grammatically correct? And if “major dumb” is grammatically correct, wouldn’t any sentence be grammatically correct, if the speaker/writer could just argue that they were using the words in correct grammatical constructions, just not in ways that people had heard before? Couldn’t I say, “The dog mailman bit” and argue that it was grammatically correct, just that “mailman” was a new verb I had coined, and “bit” was some kind of noun? I know this is all pretty farfetched, but I would like to know, essentially, what defines “grammatically correct.”

Gestalt