Off the thing he was educated in

Re "Stephen King’s ignorant tweet"

I find this applies increasingly frequently:

"There is nothing so stupid as the educated man if you get him off the thing he was educated in." -Will Rogers

Other recent examples, billionaires Warren Buffett, Sheldon Adelson and Bill Gates calling for immigration "amnesty" and Dawking and Hawkins [heh] on the reality of God.

Or, any Hollyweird celebrity speaking without a script.