> "That's a good essay isn't it?" "Yeah, Yeah." That's sarcasm, which is not a grammatical construct but a cultural(?) one. "Yeah, yeah" is a positive statemen

> "That's a good essay isn't it?" "Yeah, Yeah." That's sarcasm, which is not a grammatical construct but a cultural(?) one. "Yeah, yeah" is a positive statement (grammatically, a double positive never turns into a negative in English), but a statement said sarcastically implies that you meant the opposite of what you said.