Almost 15 years as an F/O in similar circumstances taught me a lot about being diplomatic. Treat it as an opportunity to determine the sort of Captain you won't be. It may mean pandering to these sorts to bolster either their inadequate self confidence or inflated egos ("obviously the company doesn't recognise my ability otherwise I'd be an official Training Captain") but, when you are in command, you will be all the better for it. Some words of wisdom imparted by my Training Captain when I was up for command:- "There are two types of respect. That which you Command and that which you Demand, you work out which is desirable". Unfortunately such sage-like words would obviously be lost on the types you have to endure. This advice still sticks in my mind after some 20 years and, to a degree, influences the way I work with other crew members. Doesn't mean making concessions, just determining the way you go about things.