[joshrotenberg]

Yeah but I didn't say Linguists wouldn't be able concoct a grammar for AAVE, I said one AAVE speaker would not be able to point out the grammatical errors of another.

A linguist doesn't "concoct" a grammar (not an ethical one, at least). A grammar is described based on actual usage of the language. As evidenced by the section "AAVE grammatical Aspects" in the above Wikipedia article, there are clearly rules of grammar in AAVE. What evidence do you have that one speaker of AAVE wouldn't be able to point out grammatical errors?