The long since defunct Ansett Airlines of Australia had a policy where first officers could elect not to fly with any particular captain. The F/O would merely phone in when he saw the roster and say count me out with this bastard (well, words to that effect)
There were no questions asked because it didn't happen that often. However the event would always reach the desk of management. If the same captain was the subject of more than (say) five no-fly requests by various other first officers, management twigged there must surely be a problem with this specific captain. He would be hauled in and grilled as to why F/O's were avoiding flying with him. Invariably he would have a miraculous change of attitude after that. It was a very wise policy and defused potentially serious flight deck confrontation.