Scotty: "What are ye standing around for? Do ye not know a jailbreak when ye see one!?"
Scotty: "I know this ship like the back of my hand." *bonk* Scotty: *down for the count*
And when Spock saves Kirk:
Spock: (Kirk tries to hug him) Please, Captain. Not in front of the Klingons.
McCoy, after he, Kirk and Spock were tossed in the brig, castigates Kirk for asking Spock to kill his own brother, then snarks, "Well, maybe you should toss him in the brig!" This leaves Kirk verbally defeated.
Spock: This is a new brig, Captain. Completely escape-proof. To guarantee that, they used the most intelligent, most resourceful person they could find. He was unable to escape.
Kirk: This person didn't happen to have pointed ears and a propensity for getting his shipmates into trouble, did he?
Spock: He did have pointed ears.
Piece of advice, don't eat marshmallows before hitching a ride on jetboots.
Spock: It appears we're too heavy.
McCoy: Must have been all those marshmellons.
Kirk trying to climb a mountain. And Spock suddenly showing up beside him wearing rocket boots. It's the expressions of both men which make it hilarious.
And McCoy watches from below. "Goddamn irresponsible!"
"Perhaps, "because it is there" is not sufficient reason for climbing a mountain?" "I am hardly in a position to disagree!"
"Why don't you go pester Dr. McCoy for a while?"
Sulu and Chekhov getting themselves lost while they're hiking. Not to mention their lame attempt to save their pride as they asked for directions.
Sulu: We appear to be caught up in a blizzard. (Checkov rolls his eyes, then decides to roll with it)
Chekhov: And we can't see a thing! (the look on Sulu's face as he watches Chekov make storm noises into the communicator is priceless)
And then Uhura mentions that the sensors show clear weather at their position.
Chekhov: *beat* Sulu, look. The sun's come out. It's a miracle.