This word has been the subject of much
controversy, but most authorities agree that it should never be used except in written
colloquial dialogue. In its place should be used
is it not?,
am I not? (but never the
British-
Hollywood vulgarism aren't I?),
are we not?. etc.
From the American College Encyclopedic Dictionary, vol. II (1952)
It is worth mentioning that while growing up, the usage of the word ain't would usually result in someone else reciting the following poem (or a similar variant)
Don't say ain't
Your mother will faint
Your father will fall in a bucket of paint
Your sister will cry
Your brother will die
And your dog will call the FBI