Sherlock's face though.... It's as if he doesn't want John to say that because that means someone cares for him and loves him. nd love is a human error...and John knows Sherlock thinks this...but he tells him this. And Sherlock actually seems...to be...well...broken by this. He doesn't know how to respond.
The thing that most american sherlockians don't realize is, in England "trousers" are "pants", and "pants" are "underwear". John isn't talking about Sherlock's pants he's talking about his underwear. <-- this makes it all the funnier! <-- HELP ME
That's a head canon thing I expect. But it makes a lot of sense of why Sherlock would be so darn protective of her! That is a terrible theory! But it is a great reason for them to be so protective! I would personally like to Slap Mycroft in the face now!