-----
Just because you don't say it, and just because you might not hear it among your circle of friends, does not mean it doesn't get said.
As a matter of fact, I would argue that anyone who things VAG stands for Volkwagen Auto Group, is actually the one who has never seen one.
If they know what it stands for, that just means they may be German.
Again, only complete idiots would ever say "vag". And just because one idiot says it, doesn't mean it is slang. Just because you think it every time the rest of us use it, doesn't mean it is slang.
Again, VAG isn't going to go over well in America. Agreed. But "vag" is not a slang word. It has no currency.
Aside from the trolls in this thread going on about all the... young felines that they can't stop thinking about. VAG Mafia also doesn't translate for other reasons.
The mafia part may sound cool, but the bomber mafia was a group of military officials that thought that the bomber doctrines were superior and they would've diverted resources away from fighters to bombers, believing that would, with minimal fighter support, win the war.
VAG Mafia makes it sound like a group of Volkswagen evangelicals instead of a group of enthusiasts. Something else that is common in the states are Owners Groups (OGs, and User Groups or UGs). For example, the Harley Owners Group (HOG, an acronym that they rather enjoy).
I imagine VOG would translate better, at least in the States, than VAG Mafia. Regrettably, it might narrow the scope to just Volkswagens, and not to the rest of the badges in the VAG pantheon.
p.s. I just thought of a good test of a word's currency. Can you find some bit mass market media (movies, TV show, books, something other than something someone made in their basement) that uses "vag"? I can think of multiple ones for every other slang term that I can think of.