The most common and most likely answer to this crossword clue is the 7 plus 5 letter word ALCOHOL ABUSE
I've seen this crossword clue in The Guardian
A
L
C
O
H
O
L
A
B
U
S
E
Buddy explains!
The straight part
We know that "The opposite of what AA stands for?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the opposite of what aa stands for? = alcohol abuse.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.