Sky writing??? Sorry...I'm trying to make you laugh.
As hard as it is, completely ignore him. Don't say a word. Don't justify a thing. You don't have to. People who know YOU...your friends and customers...will know the truth and see this for what it is. A little boy with a bruised ego throwing a major temper tantrum. He's making himself look like an absolute jacka$$. Rise above it. It speaks volumes about him and truly has no reflection on you whatsoever. It does however hurt.