Line checks are meant to be performed according to a standard criteria, they are not discretionary, non-technical markers assess the CRM and communications and the hands-on bit should be according to OMA/B and SOPs. Line check Captains have to adhere to standard protocol as monitored by the flight standards department/Captains, this avoids "personality issues" Politics and personal issues should not enter the environment if all parties are professional. Having said that, we are human, and if someone raises the conflict bar with constant deviations or over-confidence ,it is likely small errors may be counted as cumulative and result in a partial or fail. The line check should be as a "properly constituted crew" and is normally carried out for both pilots on the same day. If one guy passes and one guy fails then technically as a " crew" it is not a good result. The line check form should clearly detail the areas requiring attention. We often see a persons "perceived performance" and 'actual performance" are worlds apart. There is no reason a pilot cannot discuss the results of a line check with TM, debrief is a required part of the process. Nothing to do with Unions etc etc