I keep seeing it used wrong and it. is. driving. me. nuts.
PSA: "Let alone" does not mean "not even."
Here is a wrong usage: "I wouldn't follow you across the country, let alone down the street."
You could replace "let alone" here with a version of "not even": "I wouldn't follow you across the country, or even down the street." That would be correct.
That's not what "let alone" is for.
"Let alone" means "certainly not" or "especially not" or, perhaps most clearly, "much less." MUCH LESS. In other words, it's exactly the opposite of the above uses.
If you say "I wouldn't follow you across the country, much less down the street," what does that mean? I wouldn't follow you all the way across the country, probably, but I'm much less likely to follow you down the street? That's not what you mean to say, surely. You mean to make a contrast for emphasis...
"Why would I follow you all the way across the country? Dude. I wouldn't even follow you down the street!"
Correct usage: "I wouldn't follow you down the street, let alone across the country."
See? The first thing is minor...the second thing is major. It's a contrast. I wouldn't do the first thing, so I would be MUCH LESS likely to do the second, bigger version of that thing. I wouldn't EVEN follow you down the street...LET ALONE all the way across the country.
Stop using it backwards. It makes me crazy. I know you don't want to make me crazy, Internet. So stop it.
I'm here to help you stop making me crazy. You're welcome.