The Doctor had a flippant remark on the tip of his tongue. Something along the lines of Well, if it's a promise not to flirt with waiters and waitresses, absolutely not or Really, now, is this the sort of place for that sort of thing?, but the look Jack gave him made him pause. It wasn't a teasing remark, it wasn't a playful look, it was the sort of serious Jack usually held in.

Which meant teasing wasn't the right sort of a response at all.

"Course I would," he said.