Where did "...as all get out" come from?

I’ve heard people use this term in various formats. I know what they mean by context, but the words themselves seem to make no sense.

For those of you that haven’t heard this used, it’s usually something along the lines of “He was mad as all get out” (meaning he was very mad), or “I was driving as fast as all get out”. The intention of the phrase is clear, but not its history or original meaning.

Anyone?

The invaluable Dave Wilton, from an old thread in the Word Origins forum :

*“Get out” is US slang for the utmost degree. It dates to 1838. I have no explanation for why this particular phrase was used in this sense.

It’s usually constructed with “all.” Mark Twain was the first to use “all git-out” in Huck Finn, 1884.*

I miss being over at Dave’s. :::sniff:::

Since we have electronic databases now, there are earlier instances of “all git-out” well before Twain.

You’re much missed, Sam … but we know where to find you.

(You won’t escape that easily!)

I have a theory. My Mom used to say “Get out!” (said in the same tone as “No way”)when I said something that was amazing or almost unbelieveable.

Maybe the “Get out of town!” utterance of incredulity is a root for this phrase.

Thanks for the era of origin! Now, to figure out the etymology.