I have a player on my group, he knows more about 40k fluff than anybody else I know but knows absolutely nothing about RPing and so whenever we RP he messes around a lot and distracts the other players and slows down the whole RP.
Recently we had a mission that I was using as a filler mission while I was writing a new mission up and due to him distracting the others, it took us 3 sessions and even then I had to cut out a lot of what I had written for the filler because it was taking so **** long.
How would you guys deal with a player like this?