Not at all! Don't use it. The only time that it's ok to use 'ain't' is : * if you're quoting a song lyric or film dialogue etc where this word appears * if you're writing a story about characters such as uneducated farm-workers and you want to make their speech sound authentic * as a kind of joke Otherwise, you should always use the correct standard form - doesn't, hasn't, didn't, won't and so on.

It isn't grammatically correct, but if people around you are using it, then it's OK to say. Not very many English speaking areas use it though and if you say it in the wrong group of people you can come across as uneducated or having poor grammar.

No, but ignore the person who says never use it. It's used in certain parts of the UK all the time in speech.