Are you one of those folks who try to correct someone when they use the word, "ain't?" Stop. Give it up. Let it go. Get over it. "Ain't" has tenure.
I've been around long enough to see thousands of new words added to the dictionary, and hundreds more dropped. I've seen the brand name Aspirin turned in to the generic term aspirin, such that if you look at the ingredients of an aspirin bottle, it says it contains aspirin, not acetylsalicylic acid. The brand name Google is now also used as a verb* (I'm going to google his name to see who he is). The English language is not dead, it is living, expanding, ever-changing. We no longer need to appease our grandparents. Ain't is de facto common American-English. Get over it.
Any argument against the usage of the word ain't is superfelous. The dogma that one is somehow less of a person for using it is insane. Unless one is using Microsoft Office, if one keeps doing the exact same thing over and over expecting different results, one is employing insane behavior. How many folks have been saying - how many time have you been saying - over the years "Ain't isn't proper English." Well neither is answering, "Who is it?" with, "It's me!", the rules would suggest saying, "It is I." I'd bet you've never said that in your life.
If you use the word ain't occasionally, don't feel guilty. If someone has the audacity to correct you, tell them to "Get over it - ain't has tenure." If their educated enough to figure that one out - they'll understand, and if not - oh well.
In my lifetime, I think the USA may have gone from the first or second in leading scores for math and science in K-12 to probably the dead last, even behind most third-world countries. Unless these teachers go to Dubai or China to teach English, I doubt they would find higher pay, or an apropriate audience anywhere else in the world for their less-than-pragmatisic views. Let's worry less about one using the word ain't and more about arthmatic, science, and telling time (on both analog and digital clocks). There certainly is more to fix in one's own life then to try to fix another's vocabulary.
You ain't got to tell anyone not to use ain't, anymore. You have my permission.
*see reference: http://dictionary.reference.com/dic?q=google&search=search