Tertiary characters who demanded the spotlight...Do I have any? What'd I do with them? Why aren't they more important? Did they get a promotion to secondary?
Confession: I suffer greatly from the Cast of Thousands curse. I can't afford to add upstarts to the roster who shouldn't be there. Any tertiary characters--the guys who might not even have names--who somehow hog the focus of a scene during WiP drafts are usually indicators that I'm not using my secondary characters well. For me, third-string characters are either fodder or seeds planted for future books.
In short, if I have a tertiary character demanding focus he needs to shut his pie-hole or be assimilated. Resistance is futile.