"aan harf-haa" refers to "unexpected" or "unbelievable" words. In fact, "aan harf-haa" should be accompanied by adjectives like "unexpected" or "unbelievable" that they have omitted in slang conversations to form an idiom. Making same sense before and after the omission is reason of the omission!

When someone says something odd and strange, we answer : این دیگر از آن حرف هاست. or as oral we say: این دیگه از اون حرفا بودا and hear it means: start to draw again is odd and strange.