And no, it was not from anyone involved with Family Guy (I've never met the creator of that show but from what I can tell he's okay with criticism). It was a response to a much milder negative comment about something else. And no, it wasn't Richie Rich people out for revenge either.
Here's the letter, without attribution:
It was fascinating to read the critique from a true giant of mass media. I bow to your astute observation and wealth of accomplishments.
Blogging is akin to masturbation, so it's nice to see that you're truly devoted to being a full time jerk off.
I have really, truly arrived, man. The only reason to blog, nay, to live, is for people to hate you for saying mean things about them. And when they throw in a form of the cliche about how criticism is worth nothing if it comes from someone who doesn't boast a "wealth of accomplishments," it's even better. Life is good.