Rigpiggy;
I'm with you on this one. I did once watch from the jumpseat as CRM broke down between a crew and it resulted in mis-set altimeters (which the FO realised immediately, but said nothing) and left the P1 in a hell of a difficult position.
These days part of my pre-dep brief is "if you're unhappy about something, or think I'm wrong sing out quick. BUT don't be upset if I think I need to correct you.
With new FOs on type I also use "if you think you need speedbrake chances are its too late, and in that case use all of it and sort it out from there."
I'm old enough to realise that the 200hr wunderkind (and thats what I was 27 years ago) maybe better educated than me, and I often use the cruise to find out a lot of new stuff, but I need him to realise that within SOPs old age and cunning often have the edge on youth and enthusiasm.
A correction based on humour and understanding, if there's time, or done over a beer and a (relieved) laugh in the bar afterwards just seems to work for me.
SND