That's not Scalzi's Law, that's Grey's Law, a corollary to Hanlon's Razor: "Never attribute to malice that which can be adequately explained by stupidity."

As for Scalzi's Law, there are two:

Scalzi's Law of Online Communication: "Anything bad you ever write about someone online will get back to them sooner or later."

And, related:

Scalzi's Law of Internet Invocation: "If you name them, they will come."

The latter, at least, is amply proven by this comment.