"Mm. A fair point. He'd be insufferable," Sherlock responds drily, full awareness of who she means utterly irrelevant in the face of an opportunity to take a (perfectly fond) jab at John behind his back. What he isn't around to hear won't hurt him. Or get Sherlock punched again.

"'You really ought to take better care of yourself, Sherlock,'" he intones, voice raised in pitch and accent adjusted in imitation of the man in question. "'I told you you'd make yourself sick.' I told him not to eat the bloody fruit; hardly see why I have to listen if he's not going to."