From a Roger Ebert interview with John Waters (hat tip TH):
The other thing [Russ Meyer] did was attack the critics. If they said one bad thing, he would write the most hateful letters to them, which is, I believe, the exact opposite of a pro. But he was in my apartment looking through my bookshelf and I saw him lunge for this one volume and pull it out and it was The Mellons. But it was the Mellon family and he thought it was a tit book. And that summed it up. He was obsessed; he was an outsider pornographer, only soft-core. He couldn't help it.