We're now several days into a Twitter war between Harry Potter author JK Rowling and Spam-faced stupidity merchant Piers Morgan.

Morgan is fresh from a pyrrhic Twitter spat with the actor Ewan McGregor.

The new Rowling brawl started when Morgan was told to "f**k off" by Australian comedian Jim Jefferies during a debate about Donald Trump's travel ban on Real Time with Bill Maher.

The clip went viral, helped on by JK Rowling.

Morgan turned to the Twitter Comebacks chapter in his well-thumbed copy of The Big Boy's Book of Classless Petulance.

Then it got really cringeworthy. Morgan called Rowling out for "priceless humblebrag BS" when she tweeted a gushing blurb about her success. Take a guess who wrote it.

Maybe Morgan should have read Harry Potter, though he's being helped by one book shop which is tweeting The Philosopher's Stone at him.

But if he knew Twitter better, he'd have held back from lashing out at Rowling. She doesn't take prisoners.