Sherlock Spills the Beans

Sherlock blurts out some private details about John's sexual habits, during a case, in front of Greg and Sally. John is furious that Sherlock would let the Yard assume he had first-hand knowledge of John's behavior in bed, but Sherlock doesn't see what the problem is - he's deduced everything already, so why hide it? Especially when he's got some suggestions of his own . . .