Depends on your audience. I write for a living, and, as a general rule, I don't use AINT. However, If I were trying to be folksy (in other words, laid back, loose, etc.), I would certainly use it. This is because it is sooooo common in the USA, and it means you are "shootin straight" with somebody, or "being frank". I might look at one of my high school students who keeps talking out of turn, and say, "I ain't gonna put up with that much longer." The student would know that I was being direct and frank, and would likely start raising his hand when he wanted to speak. We need to throw away our dictionaries at times, and focus more on conveying a thought in a way that it will be properly understood. That's why I nearly never use WHOM in speech (unless it comes after a preposition). I want to be seen as communicating, and not trying to impress somebody with my grandiose language skills. It all depends on one's audience. In other words, don't show up in a tuxedo to an outdoor swimming party - unless you want to look like an idiot. On a basketball court, players use quick, efficient slang. When they are open to take a shot, they simply yell YO. They don't say, "Excuse me, Frank, I am available to attempt a field goal, so could you please toss me the ball when it is convenient for you." A thought needs to be conveyed. On a basketball court there is no time to care what the grammarians of the world may think of you. The phrase AINT THAT A SHAME is very acceptable by the way. Most writers would not dare use it, but EVERYBODY in the English speaking world clearly knows what it means. So, why we consider it "wrong" bewilders me. People forget that "AREN'T I" makes NO logical sense. I is a singular word, and ARE is a plural word. A long time ago, we used to say AM NOT I, or AMN'T I. This was replaced by the head-scratcher AREN'T I. After all, you would never say this: Isn't it the case that I are going, too? So, then, why is it okay to say this: I am going to AREN'T I? In that sentence we change the conjugation from am to are after just TWO WORDS! Somehow, this lunacy became acceptable. Now, ain't is a much more logical conjugation than aren't. At any rate, I ain't gonna use ain't much cause ain't ain't accepted by most right thinkin people.
