My people said "fixin' to" and "crick" and "I'll swan," -- there's some linguistic overlap between south and deep midwest.

"I'll swan,"

What does that one mean? I always read it in books when I was a kid, and I could never map it onto any phrase that I know.

for when you really want to swear, but can't admit it. It has the added advantage of sounding as if you might faint.

It has the added advantage of sounding as if you might faint.

In a graceful manner - i.e. more like a swan than a duck.

always. though if you do it too much, you'll most likely come down with the vapors.

or an overwhelming sense of self-importance.

"Might could" and "might should" are right up there with "y'all" and "fixin' to" as Southernisms I can't talk without. I also sometimes say "they's" when I mean "there's," but I've almost trained myself out of it, and it only comes out when I'm very tired or distracted.

According to this post,

The Oxford English Dictionary has "swan" as a verb, labeled U.S. slang, derived probably (it says) from northern England dialectal "Is' wan," literally "I shall warrant" = I'll be bound; later taken as a mincing substitute for "swear." The first use in print recorded in the dictionary is from the year 1823.

A Southernism that fools me every time is when you ask a Southerner if they know where something's at, and they reply, "I sure don't!" Northerers I've known only say "I sure do" and never use the negative, so it's confusing when you're expecting something helpful at the beginning of the sentence, only to be skunked out by that final "don't!"

"a mincing substitute". That's a lovely phrase.

Hooray! I finally got a Cook's Illustrated test recipe that I can actually make.

I didn't realize the breaking your ethnicity into fractions was a Chicago thing. My Mom is from Chicago but she totally does the small talk with strangers thing. Maybe that's just Mom but my friend John, also born and raised in Chicago usually manages to get the life story of every cab driver.