Over the years, sixteen to be exact. That's when the Hogwarts prefects started mumbling about "adding that to the list". When Professor McGonagall pulled the prefects that were complaining about the rounds on the train, she indicated to them that they were "lazy, exaggerate rating, and not worthy of the job". After a year of not receiving this "list" of theirs, she just perceived the whole thing as a bluff. Then finally sixteen years later, that year's Head boy and Head girls handed in the list full of complaints to her. The list was quite detailed and explained how many of these events took place. Everyone of the houses signed off on it, even Slytherin House that was a shock in it's self considering they never agree with Gryffindor students.
They handed her the list and then left her office. The professor quickly glanced at the title and even a no nonsense type like her had to laugh. The list was titled The Stupid Things First Years Do On The Hogwarts Express.