Kirk has this habit of abandoning the bridge whenever some sort of critical or potentially dangerous ship operations are about to happen. It's not the first time we've seen this behaviour.

Also: Clearly I need more practice drawing people from behind.

Transcript

1
Captain's log, Stardate 1512.2. Crew are playing a game of Annoy Spock.
Sulu: Object approaching at light speed. No visual contact yet.
Spock: Really?
2
Sulu: It's a 107 metre cube. Mass 11,000 metric tons.
Scotty: Must be solid metal.
Spock: That's a density of just 8.979—
Scotty: Solid metal, I say!
3a
Bailey: Let's blast it!
Spock: Your enthusiasm noted, Mr Bailey. Captain to the bridge, immediately!
3a
Kirk: I'll just roam the ship with my shirt off a bit more first.
4
Spock: The cube won't let us past. Suggest we reverse.
Kirk: Plot a spiral course around it, Mr Sulu.
Spock: Reverse would be—
Kirk: Boring!
5
Bailey: Destroy the cube!
Spock: Radiation increasing.
Bailey: Destroy it!
Spock: Radiation lethal.
Bailey: Destroy!
Spock: Radiation more lethal.
Kirk: Magic word, Bailey?
6
Captain's log. Cube destroyed. Advancing into further danger. Time to go get drunk with Dr McCoy.
Kirk: Run drills while I'm gone. I want these men exhausted!
Spock: But—
Kirk: Drills!
7
Sulu: New ship, sir.
Balok: I am Balok! I will destroy you! In 10 minutes!
Spock: He reminds me of my father.
Kirk: Damn! Okay, Balok, you win this round.
8
Spock: We cannot break free. We are outplayed. Checkmate.
Kirk: Not chess... poker! Booya! I'm back in the game!
9
Kirk: Go ahead, Balok. Our corbomite device will reflect your attack and destroy you!
Spock: Corbomite? What—
Kirk: Shhhh!!
10
Balok: You win.
Kirk: Break free!
Spock: We are overheating.
Kirk: More power!
Spock: Engines 2000° above maximum. That should not—
Kirk: More power!!
11
Uhura: Captain. Distress signal from Balok.
Kirk: I'll beam over, with McCoy and Bailey.
Spock: Request permission to—
Kirk: Denied. If it's a trap, I want Bailey to be the one with me!
12
Balok: I am Balok. You saw my puppet before. It was all a test to see if you were peaceful.
Kirk: You were peaceful all along? That'll annoy Spock.
Balok: I win! Two out of three!
Kirk: Damn!