I know "Spock's Brain" is often cited as far and away the worst episode of Star Trek, but for me this one is right up there, at least on par. At least "Spock's Brain" is merely outlandishly silly and can be enjoyed in a camp sort of way. This episode is just cringe-worthy. It probably makes it worse for me that the blatant jingoism of the ending is jingoism for a country not my own.

I didn't have room to include the yet-another involuntary fight to the death between Kirk and a fellow Starfleet officer - this time Captain Tracey.

Transcript

1
Captain's log, Stardate 4695.1. USS Exeter is adrift around Omega IV. Beaming over with no quarantine precautions.
2
{On board the USS Exeter}
McCoy: These crystals are all that's left of them. Everyone knows the human body is 96% water.
Spock: You mean 65%.
McCoy: Who's the doctor here?!
3
Spock: Last log entry, captain.
Exeter Doctor: You're DOOMED! There's an infection. Your only chance is to beam down, fast!
McCoy: PLAGUE!
4
{On the planet Omega IV}
Kirk: Captain Tracey!
Tracey: I'm the last man alive. The planet's surface gives an immunity from the infection.
McCoy: Awwww...
5
Tracey: These are Kohms, a peaceful primitive civilisation. And these are Yangs, violent savages.
Kohm: We beat them back with fire boxes!
6
Kirk: Tracey gave them phasers. He violated the Prime Directive. Unforgiveable!
Spock: And how often have—
Kirk: Not important!
7
Kirk: Tracey! You may lock me in a cell, but you'll never take my freedom!
Cloud William: Freedom? This is Yang worship word.
Kirk: What, really?
8
McCoy: Jim, these races fought a biological war that took them back to the Iron Age. The survivors developed immunity, like we have.
Spock: That makes no—
McCoy: Like we have!
9
Tracey: This Yang you helped escape led a massacre of the Kohms!
Cloud William: We have taken our own land back.
10
Kirk: Wait. "Yangs"? Yankees!
Spock: And "Kohms". Communists.
Kirk: It's all so obvious!
11
Cloud William: {holding a US flag} Behold our holy artefacts! Ay plegli ianectu flaggen-
Kirk: ... to the Republic for which it stands...
Spock: This makes no—
Kirk: With liberty and justice for all!
12
{Enterprise bridge}
Kirk: All's well that ends well.
McCoy: We just let analogue Americans wipe out analogue Communists.
Kirk: And an allegory too! Yet another job well done!