Where I work it happens from time to time that CDR's are flying together. If it's planned from the beginning. The guy with the highest seniority gets the left seat. On the other hand, if there is no F/O available due to eg. a sick F/O, and no other F/O's available to replace him, the captain who is called on sby gets the R/H seat, and functions as a F/O regardless of seniority -even if this is the chiefpilot himself.
I have been a captain for seven yrs, and have no difficulties to have a more senior colleague as F/O. Nor do I have any problems
to serve as a F/O to a less senior captain.
In a situation if I as a CDR is making a bad decision, I expect the
F/O to correct me. I will not "loose face". I would rather greet him for doing his job.
In my world, this is what CRM is all about.
Likevise, when I read flight occurency reports, I try to learn from
other people's mistakes. Not condemn the guys involved.
Blue skies!