We start out this chapter learning about how dangerous poetry can be. Vogon poetry is the third worst and most dangerous. The second worst poetry—the Azagoth's poetry—could make people die of internal bleeding.
The worst poetry in the galaxy is by Paula Nancy Millstone Jennings, who lived in Greenbridge, in Essex, in England, on Earth.
So it's bad news for Arthur and Ford when Prostetnic Vogon Jeltz starts to read his poetry to them. Especially because they are strapped into "Poetry Appreciation Chairs" and have other devices hooked up to make sure they really get the poetry.
Ford and Arthur suffer through the poetry—or as the British say, lorry flat lift.
And then Jeltz gives them a choice: be thrown out the airlock or tell him how good his poetry is, which sure makes him seem like some people we know.
Arthur valiantly tries, telling Jeltz that the poem had some very nice "metaphysical imagery" and "interesting rhythmic devices" (7.22, 25). In other words, Arthur makes up a bunch of stuff in order to make it look like he understood and liked the poem, whereas most people just choose the simple solution of saying it was "interesting."
Jeltz doesn't fall for it. Arthur and Ford say the poem shows that Jeltz has got a good heart, but Jeltz knows that he's rotten to the core.
So Jeltz orders Arthur and Ford thrown off the ship. Everyone lives happily ever after, except for Ford and Arthur, who die in the cold void of space. No, wait, that can't be right.
What actually happens is that Ford almost convinces the Vogon guard that there's more to life than throwing people out of airlocks. Almost, but not quite.
So the Vogon guard throws them into an airlock. So, as Arthur keeps repeating, they're really going to die this time, 30 seconds after the airlock opens.