Nah ah ah
A stupid, annoying way to say you're not buying it. Like you're too cool to even care. It sounds like a kid who failed math and still thinks they're the best.
My homie said 'Nah ah ah' when I told him I beat him at Fortnite.
My mom used 'Nah ah ah' when I said I didn't eat her favorite cookies.
My teacher said 'Nah ah ah' when I said I didn't do my homework.