Scotty declaring that the ship about to blo apaart, and then it does just that.
An alien, augment, or opponent of the week declaring to Kirk as they are about to fight that he has five times Kirk's physical prowess and then proceeding to methodically beat the shit out of him.
An alien race or being taking over the Enterprise without effective resistance but then realizing they haven't the knowledge, training, or even the foggiest fucking clue as how to even begin to operate it.
Kirk ordering the Enterprise to execute a back-in-time-around-the-sun-or-whatever maneuver back to the 1930's so that he can beam up Edith Keeler just as she is about to get mowed down in that auto accident; and then later making a return trip to beam her back down into the auto accident when he realizes it was all a big mistake, they are really different people, and things just aren't going to work out and he really doesn't want her getting 50% of his shit.
Spock commandeering the Enterprise to execute a back-in-time-around-the-sun-or-whatever (bitatsow) maneuver back to a dead planet's ice age to retrieve his favorite has-been hottie only to grow weary of her constant demand that he continue to eat animal flesh; return again back in time and beam her down to 1930's San Francisco to die with Edith Keeler in the auto accident.
Kirk and Spock making a bet over who could be first to go back in time and insert themselves Forrest Gump style in some historical photograph; but the bet falling through when they can't agree on the meaning of "first" when time travel is possible.
Spock telling a joke.
Spock understanding a joke.