3. "Where Are They?" 'Hound Of The Baskervilles'
Sherlock's drug habit remains pretty subtext in most of the episodes. Instead, what comes up is his smoking habit. Smoking is bad for you, and in London it's very difficult thanks to various legislation. So, when we see Sherlock having a craving, it's for cigarettes. Nicotine patches just aren't as good as having a good smoke. When faced with boredom even after spearing a pig with a harpoon Sherlock desperately needs a cigarette. But he, and his friends, have outsmarted the craving. So he's reduced to bouncing around the flat looking for a smoke, to screaming at Mrs. Hudson and Sherlock, and almost to playing Cluedo. The entire scene is bonkers, compounded by his insane intensity when his client starts smoking. The man's stoicism is pretty impressive, given that a crazy man is invading his personal bubble to inhale desperately. We see Sherlock get nutty several times, perhaps most memorably when he stole John's gun and attacked the smiley face in the wall. But this one is definitely the funniest example of how Sherlock's way of looking at the world can result in a person who is clearly freaking insane.