Lets put the boot on the other foot.
Same scenario as posted earlier about the Cb's. FO is PF and the skipper is PNF. FO (PF) looks at radar and the upper level winds and decides he would like to go 20nm right of track to get around the Cb's, the captain looks at the radar and says nah you don't need that much i'll ask for 10nm, we got a schedule to keep.
and scenario 2.
FO is PF again and skipper PNF, the FO gives his/her descent and approach brief, says he's going to fly the RNAV approach, captain turns around and says nah mate just do the DGA and circle back around onto the runway, doing the RNAV will make us 5 minutes late. And then on the DGA tells the FO what the descent point will be.
What does the FO do? sit there shutup and accept that he's the captain and he should know best and do as he/she is told? or say I'm PF I would like to fly the RNAV?