That is a fair grammatical pet peeve. I have a pet peeve for when people use words for the exact opposite of their meaning. Not just your classic "could care less", or other things that mostly just come from people mishearing the correct phrase, but using entirely different words whose definition literally means the opposite of what they mean.

A couple examples:

1. I had a Facebook friend talk about how, before he went on a trip overseas for a few months, like 30 people threw him a surprise going away party. He described this event as "humbling". Yeah, that giant group of people coming out to celebrate you in particular and personally send you off on your trip must have really took you down a peg. I'm sure it really lowered your ego and made you realize you aren't important.

2. I CONSTANTLY hear in tv shows and movies stuff like "I'm really anxious to get going. I've been looking forward to this all week." The word is "eager". You are eager for something good that you have been anticipating. You are only anxious for some upcoming event that you are dreading or that you are trying to avoid, something causing you anxiety, thus the word. You are anxious for the upcoming test you arent prepared for and you are anxious to escape the haunted house without screaming like a little girl at a jump scare. You are not anxious to earn a payraise.

I wanted to highlight that this use of "let alone" is only for the negative construction where "let alone" means the same thing as "much less".

In a more positive construction "let alone" means the same as "not to mention" while both not letting it alone and still mentioning it. The earliest reference in the OED is of this construction:

“I didn’t hide, nor wouldn’t from any man living, let alone any woman.”

Before this use, to "let alone" was to "leave alone" and dates back to the old English.

I'm not sure when the negative construction of "let alone" first emerged, but it's no more than two hundred or so years old.

It's not my pet peeve, but it does irk me. I'll stand with you against the wronglings.

Thanks for this, we don't want to loose sight of the correct usage.

Grammar changes, nobody really cares except linguists, let alone the common English speaker.

https://www.cambridge.org/elt/blog/2020/02/12/language-evolution-reflecting-language-change-darwin-day/

Reading internet comments is a terrible addiction. Having to see people using language wrong, and realizing it's almost always a native speaker is just one of the pains it brings you.

Shouldn't the content warning be for Prescriptivism?

Prescriptivism is prescribing how language should or should not be used, and is generally avoided by all linguists who aren't 19thC european aristocrats intent on using language as a class marker.

Descriptivism is just describing how language is used by its speakers, without passing judgement.

English language learner here. Would "let alone" basically have the same meaning than "not to mention"?

Off my chest - if you're the kind of person that necessitates a content warning on this kind of post, you should be banned from the internet

Your literally making a mountain out of an anthill, let alone slightly overexeggerating a tiny nonissue. Get out of here with you're language policing. Grammer nazis like you should be thrown into the specific ocean.

Nobody who speaks English as their native language is using the idiom incorrectly.

They might not be using it traditionally, but if it parses it flies