This was very bittersweet; he thought they were all crying because he had done something wrong, it didn't cross his mind that he would ever make someone cry tears of happiness." --Yeah, I didn't need my heart in one piece.
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. One of my favorite scenes.