She may have said it that way for Jack's benefit, and to tease them. "Aww, is the Doctor afraid of getting spanked~?"

Well he probably should be, but regardless she doesn't intend to let Rose end this evening doing something she might regret if she can help it, since she's the one providing the booze. "Jack, Jack, Jack, It's one thing to point out what the entire bar can see, it's another to try to hop on in."