It is interesting hearing people use "aren't" incorrectly in attempt to be correct by avoiding "ain't." Such as, "I am supposed to be here, aren't I?"

"I am supposed to be here, are I not?" That obviously is not correct. If they had used "ain't," they would have been gramatically correct: "I am supposed to be here, am I not?"

"Ain't" is informal, but it is not always incorrect. It is a contraction of "am not," and in places where "am not" is correct, "ain't" is also correct.