1) Specific - AU. John goes to the Yard, not sure why, and walks past a room where Sherlock is talking to Lestrade about a case, and John says, "Maybe it was the sister. Because who else would he trust to make the tea? His sister." And then leaves.
A few weeks later the Yarders drag John into the station because he killed a guy who was trying to rob a woman and child in an alley. He finds out that Sherlock is there, and goes to find him. Then John deduces everything about him. Sherlock is very impressed.
Found: The Doctor1b) I'm also looking of any sociopath!John fics. I recently read one, and that has made me very intrigued by the idea.
2) Specific - John bought Sherlock a Christmas present, but it was in a safe, that was booby trapped, and stored in boxes... etc. Because he wanted Sherlock to have a puzzle to work out rather than just a boring gift.
Found: Christmas Fluff