How to deal with a geek who knows a lot about a RPG setting

I've run into this with a person in one of my RP groups, who knows a lot about history.
The way to stop someone like that from giving you a hard time, is to know at least a fair amount about the place/time that your role playing in. And you can always tell him/her that it is YOUR game and you can do what you like with it. If that still doesn't work, try talking one on one with him/her, saying (diplomatically) if they would PLEASE give you a break.
And that worked for me :)

Simon