His smiles when he gets annoyed.
GUH.
I LOVE HIS ANGRY SMILES. They are one of my favorite things about John Watson. He’s got so much angry in that short frame of his, and it’s so very rarely aimed at Sherlock (but it is sometimes; John never backs down from Sherlock when he’s got an opinion beyond “I’m so charmed by watching you that I can’t think straight”). I adore it.