During the Mirror Universe incident, Mirror Spock implants in McCoy a trigger phrase that helps spark something later on
McCoy can be quite the hypnotist when he wants to, and as Kirk experiences first-hand.
Mirror Universe Saga Part 1: Kirk and M'Benga use a mind control drug to get revenge on McCoy in the form of Spock
Mirror Universe Saga Part 2: As part of a Vulcan ritual, McCoy is turned into a she-male and turned submissive by Vulcan techniques
Mirror Universe Saga Part 3: Spock reinforces his control on McCoy and Kirk attempts to use similar measures to win him over
Mirror Universe Saga Part 4: McCoy goes to Vulcan where Sarek brainwashes him completely to turn him into the love toy of the household
In Star Trek V, Sybok brainwashes McCoy and in order to win him back, Spock employs similar measures
After the encounter in the Mirror Universe, a man takes advantage of McCoy's wounded brain and Spock has to come to his rescue
In the Mirror Universe, Spock brainwashes McCoy and turns him into his slave
Chapel finds Spock and McCoy under the effects of a drug that controls their minds through arousal
Mirror Spock uses an hypnotic agent on Mirror McCoy to make him into a sr'ben
McCoy fantasizes about the mind-rape that occurred in the Mirror Universe
The Klingons kidnap McCoy and brainwash him to believe he is a slave
The Romulans use mind-rape on McCoy to discover his unspoken truths.