Trubru,
I am a CRMI and you are unfortunately experiencing one of my typical examples of the modern generation and the most difficult situation for any of us to deal with.
I also believe the advice of fullyspooled is good. However letting someone fail in the environment of the RAF on a training sortie and doing the same thing where we have to deliver in the corporate world are different challenges. I recently had a copilot who was questioning and suggesting a better way to do everything right down to making the tea. After he suggested to the aircraft owner one day we do somethings differently I let him managage a constant descent to visual approach at an international which he completely messed up and made things very uncomfortable for the boss down the back, credibility was restablished. But it is not normally a good idea to subject the pax to the exercise. Fortunately the boss saw exactly what was happening.
If he has been with you for 10 months it may be a good idea to deliver his annual appraisal such that any probation period is extended until he improves his interpersonal skills. Under UK law you can instantly dismiss an employee without any reason upto 12 months from employment. Beyond that you need a track record so it could be worth starting a documented record.
I hope the many copilots who read this will understand that supporting your captain is the most important role they have. Any increase in pressure will sap the captains ability as he will spend too much time worring about what you are going to do next and what problems it will cause him.
Learn to make the tea and do it well, then each time the Capt offers you a new challenge do it just as he asks and do it well. Then in time you will understand what we are talking about.
All the best Trubru, you have my sympathy
MM