1. Sherlock won't say 'bless you' if you sneeze. He thinks that it's a ridiculous and outdated pagan custom, and if you pick him up on it will submit you to a brief yet acidic lecture upon the fact.
2. After watching an old Frankenstein film together one evening, John was only able to dissuade Sherlock from stitching together his own creature from the various body parts lying around the flat by threatening to tell Mycroft. After which Sherlock sulked for a week and then deleted the film from his memory.
3. Sherlock rarely remembers birthdays. A couple of years he's even forgotten that it's his own.
4. Sherlock has never learned to drive. Not because he wouldn't be perfectly good at it, or because he lacks the money for lessons, but for the simple reason that all of that knowledge would have to take the place of something absolutely vital, like the decomposition rate of a body when left out at exactly room temperature.
5. He has never really understood why John has strictly forbidden him from informing Anderson's wife of her husband's extra-curricular activities with Sergeant Donovan. He especially doesn't see why he isn't allowed to explain why Anderson prefers Donovan over her. It'd be for her own good.
6. When Sherlock was thirteen he was very nearly expelled for unintentionally melting a hole through the linoleum flooring of the Chemistry classroom. His defence? He was testing to see if a combination of weaker alkalis, such as toothpaste and washing powder, would neutralise a stronger acid - such as the hydrochloric acid locked securely away in the teacher's storeroom. It didn't.
7. After Lestrade's impromptu and highly uncalled for drugs bust, Sherlock's stash of not-exactly-legal substances is concealed somewhere so secret that even the omnipresent Mycroft hasn't found it. Yet.
There were going to be ten facts, but inspiration drought hit after the seventh fact and I'm going away for a few days without internet so I wanted to get it posted up. So on that basis there very well might be another little chapter like this when I think of some more facts.