I am sure that this is something that every GM has had to say at on time or another. I have had to say it a few times in my GM life. As a GM you are responsible for so much within the game. You have to create NPC’s, worlds, encounters, items, the story, background and so much more.
Imagine that you have come up with a campaign, or even a one shot and all your players are “rolling” their characters. The players have thought long and hard about what and who they want to play. They are asking you questions about the world and getting some feedback from you. Then one of them says, “I am playing Ninja.” The others roll their eyes again. You know that this conversation will not go well. You say, “There are no Ninjas in this world. There are no martial arts or anything like that.” The Ninja responds with, “Yeah but I want to play a Ninja. I can be the only one in the world.” So again you say no to the Ninja. Though the Ninja will not let it go and insists that is the only thing he could come up with and really wanted to play this time. This argument goes on for a while and the others have finished their characters and are ready to play.
As a GM you have spent so much time on preparation and made no allowances for Ninjas, Jedi’s, Vampires or the like. You are pissed!
I have done two things with this dilemma over the years. The first is to say, you can create a character as close to a Ninja as possible (without everything that a Ninja has or knows). The character also cannot be called a Ninja. This compromise never really works. “How can you be a Ninja without all the Ninja stuff?”, is their response.
The second is to say, “No, no, no and no.” Then I bring the others into the argument. I put it to a vote or let peer pressure take over. This is the solution that works for often than not.
Now I see this player that always wants to play a Ninja, Jedi or Vampire as a douche-bag! I have found that the player needs to be shown how great roleplaying games can be for them. Once they see the potential, the Ninja in every setting goes away.

Have you ever read the Ab3 stories? There’s a recurring character in them who does his best to cobble a ninja together in every game the group plays, regardless of the amount of sense it does or does not make.
I have not read the rants. I just went to the site and saw there are a few of them. I will have to read them. Thanks for the link.
I was thinking today about how there was always someone who had to play that Ninja. Kind of hilarious after I think about it.
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