from Devil in the Dark:
Spock: silence while initiating mind meld then....AAAAHHHH!!!......PAIN!
It's even funnier if you're familiar with a little story behind the shooting of the scene. According to Nimoy, Shatner's father died during the shooting of that episode and he had to leave. When he returned to finish his shots for that episode, they included a shot of Kirk reacting to Spock involved in the meld. Shatner insisted that Nimoy fully act it out for him, and when he shouted "Pain! Pain!", Shatner yelled, "For god's sake, would someone get this man an aspirin?!"
I tend to laugh at a lot of of the wardrobe and hairstyles of the aliens. Of course, that's a recurring theme.