Mild - he tells Spock that Spock wanted to have this opportunity to replace Kirk as captain, that McCoy would replace Spock if it was in his power and at every opportunity he tells Spock I told you so.Was it violent when Spock yanked a recovering McCoy up on his feet, then shoved him back down, or was beginning to strangle McCoy over his demanding answers out of Zarabeth in "All Our Yesterdays""? If the answer is in the neighborhood of "Well, he was not 'prepared' to exist in that world's past, so he was regressing to his violent ancestors' tendencies", then I will remind you that McCoy was just as under the influence of the Tholian's space, which--again--was so psychologically damaging that it led to the Defiant crew killing each other...but McCoy's actions in the episode were nowhere near that level-- mild, and Spock did not nearly fall out of the captain's chair.
In Yesterday McCoy makes a racial slur against Spock, calls Spock dishonest, tells Spock Zarabeth would lie, steal and cheat and murder Captain Kirk who she never has and never will see (actually I never understood McCoys attack on Zarabeth here) - poor recovering McCoy so innocent.
