Over 10 years ago saying "ain't" was discouraged but it was gaining momentum. What happened? Seems like it's still discouraged. Maybe in another 10 years?
After centuries of being denigrated by schoolmarms the word “ain’t” has taken up a unusual position in the English language.
It is a word that almost embodies the essence of informality in language. Using it means that you consider the discourse context to be one of extreme informality, or when using it in a context which is already quite formal, it serves to lighten the mood or to inject a degree of folksiness.
I would never use "ain't" in any kind of formal communication, written or spoken.
The only time I could see myself using this would be when directly quoting someone else, or when attempting to mimic informal spoken use in something like a message to a friend. For example,
You want me to give you all my beer? That ain't gonna happen, boy!
I spent most of my life believing 'ain't' was just a colloquialism/dialict whatever but noticed a couple of years ago when reading a classic Victorian novel (I can't remember which as I read a lot of this type of literature - and it could actually be that I noticed it in more than one such novel) that characters portrayed as very respectable upper and middle class used 'ain't'. I noticed it because from a modern viewpoint it seemed quite jarring coming from them.
I will endeavour to find out in which novel or novels I saw this.