JAR Ops makes the chain quite clear:
1 - The aircraft commander
2 - Any other operating Captain
3 - Senior First Officer
4 - First Officer
5 - Second Officer
6 - Senior Cabin Crew Member
Many tasks are delegated to the Senior Cabin Crew memeber, but ultimately the buck stops at the sharp end.
I would hope that in this day crew of all ranks can see the big picture and work together in a well mannered fashion.