It really bothers me that the case of the bloody guard or whatever it was called was selected at random when Mary got Watson to convince Sherlock to take on a case, and this was one of the stories selected to tell at the best mans speech at random again, in total coincidence to the fact that it was related to what was going to happen.
Considering Sherlock has a ''conversation'' with his brother in his head about how there are no such thing as coincidences during the speech scene I think is no coincidence.
Also, I doubt Mrs Hudson would have let the ''girl who dated a ghost'' up into the flat when she knew that Watson and Sherlock were having the stag party and were already drunk.....but that's a small annoyance.