Anyone who has smacked a bare foot against a table leg will recognize the feeling at the heart of this short three-line poem. The speaker declares that stubbing your toes is the worst of all horrors, and then goes even further, saying death would be welcomed. It's an obvious exaggeration, and that's the joke. A tiny, brief injury gets treated as if it were the greatest catastrophe imaginable.
The speaker sounds dramatic and fed up, but not truly despairing. The humor comes from the gap between the grand, serious language ("horrors," "death") and the small, silly cause. The poem's compact form helps, too: the first line sets up a big claim, the second makes it more absurd, and the last delivers the punchline. The mood is playful and relatable, a little like a groan you let out in the moment, when the pain is sharp enough that overreacting feels completely reasonable.