This is kind of a funny statement to make, because he wasn’t particularly charming at all, was he. He was being a show-off. There was the fake smile, the deductions, borrowing John’s phone, a riding crop in the mortuary, and the probably embarrassing comment about John’s psychosomatic limp. But it’s really sweet that John was charmed, don’t you think? John was charmed on sight, and Sherlock was keen to impress him with 221b, and got all flustered when John thought the place was a mess.
This might be them flirting. Oh, puppy love. <3