My profession dedicates itself to the proper use of words. I also grew up in a family and a toney suburb where "proper" English was the only acceptable kind.
Nonetheless, I love how slang often does not mean the same thing as its nearest "proper" phrase. Many "aints" simply mean "is not," but there is a subtle use of "aint" that conveys a different message than "is not." "That aint right." has a slightly different meaning than "That is not right." There's a feel to it that, while close, is not the same. "Aint that a B-----" definitely conveys a different message than "is that not a B-----."
I spent a significant amount of time in my early 20s around people who use y'all regularly, and I found I liked it. I don't use y'all very often these days, but I still use it from time to time because it works.
I've always recoiled against irregardless for all the same reasons stated here, but the upbringing and circumstances that lead someone to use that word probably shouldn't be held against them.
I distinguish between less and fewer, and have all kinds of other silly preferences, but fundamentally, that's what they are: silly preferences. As long as we understand each other, I'm good.
As an aside, a curious question as it relates to the goings on in the travel thread: is a Californian a Yankee? I've thought of myself as one, but only in the dumbest, most irrelevant sense of being not Southern and pro Union (1861-1865). What difference does that make? It's not like I had a vote. Overseas anyone who is an American is a Yankee, but I suppose Southerners probably don't like that. But the more I've become acquainted with New England and the Midwest, I'm not sure that Mainers are "Yankees," nor, necessarily are Midwesterners. Is a Nevadan a Yankee? California was actually relatively pro-Southern during the Civil War (and before it); are we Yankees? I'm sure as heck not a fan of the baseball team by that name, nor, particularly, the city that hosts that team. (I don't hate New York, but it's not my favorite.) Bostonians might also recoil at being called Yankees.
Anyway, now I'm just prattling on, so I'll stop.