The F/O clearly doesn't have a clue about what his duties are.
He needs a rude awakening into real life and I would as a commander wait until being on ground and then let him know in a very exact manner what I'm not happy with. There are a couple of things one has to considder though:
1) do I have to do further flights with the same copilot on that same day?
2) how much experience does the F/O have?
3) does he show other signs of not being in the game as regards to begin a good colleague?
If I have to do further flights with him, I'd go easy. You don't want to create a bigger problem than it really is. Telling someone you're not happy will envoke hard feelings so it has to be done in such a way that that persons performance isn't decreased. If I bring my colleague down, I bring my self down...
That's where experience comes in. An FO with 2-3000 hours will have a broader base to stand on when someone tries to change his/her behaviour. It may be a good thing but it can also be bad. Good because there will be some substance in subsequent discussions. Bad because his behaviour will be more rigid than an F/O with 200 hours.
And if he's a friendly dude otherwise and just happened to fail on this item, then there's a good chance that only a small hint will be enough to set him off in the right direction.
I flew with a captain that called field in sight when I was still happily cruising along at level with 70 miles to go and no field in sight what so ever. It resulted in a missed appch because he, in effect, took control over the flight without keeping me in the loop. I was actually furious, but because he's a decent guy otherwise, I decided to ask him what his views on calling visual approaches were. As he explained, I began to understand his way of thinking and I then began to explain my view and tried to make him understand that if I'm flying the the plane, I want to be in control of when my IFR approach becomes a visual approach. He didn't understand my point, but what I made him understand was that it is very important to me that things are handled that way. I never raised my voice and never showed signs of irritation, only very exact comments. In the end he agreed to never call for a visual approach unless I'd said that I had the field in sight, eventhough in his world it was just nonsense.
Perhaps this could be a way for you to handle that F/O. Ask him what his thoughts are, make him ventilate what he was thinking and then explain to him what your thoughts were in that situation. Explain that it is important to you that he shows that he's able to execute your commands. If that's during cruise, what about if something catches fire and you're forced to take "uncomfortable action" in some way. He might not understand, but if you explain that it's important to YOU, he has to follow it. As long as you argue with facts about WX avidance and company regulations he will allways be able to mouth back. But for personal preferences, he can't say anything.
/LnS