"Aren't I?"

The assertion that the word ain't is improper is an erroneous assertion. "Ain't" is a contraction of "am not," and therefore it is properly used in informal conversation in that context. It is not, however, a formal word and should never be used in any sort of formal language.

It sometimes is ludicrous to listen to people try to avoid using "ain't." For example, one might say, "I am your brother, aren't I?" Aren't is a contraction of "are not," and thus what he just said was, "I am your brother, are I not?" Why substitute incorrect grammar for correct grammar, even if the correct grammar is informal?

The sentence, "I ain't going to do it," is an entirely correct sentence grammatically.