Touring radio stations to trumpet the latest economic figures, he wound up BBC presenter Lisa McCormick by repeatedly referring to how well the economy was doing on Tyneside.
"You keep mentioning the River Tyne," she finally snapped. "That's not our region Prime Minister. I'm sorry, we are the River Tees."
Mr Cameron replied: "I'm sorry, I thought I was doing ...." before going on hastily to point out the Government was, in fact, investing £90million in the Tees Valley.
But that did nothing to placate Ms McCormick, who noted how it was putting £470m into Manchester and £440m into South East England.