I find it kind of creepy and unethical that Spock would ever do that, to be honest. To reach out and erase someone's memories.
I'll offer up these two for consideration. Both are "Kirk Moments".
The first is when he orders Spock to relieve Decker "on my personal
authority as Captain of the Enterprise
..." Shatner simply sells
that He's The Captian, in that scene.
My other contender would be his "In every revolution..." speech in Mirror, Mirror.
Too bad that the PTB years later would waste that moment with the BS that was DS9's Mirror episodes.
ETA: I see JSC beat me to the Personal Authority scene...