My friend keeps saying 'cheer up, it could be worse, you could be stuck underground in a hole full of water.'

This one-liner gets its chuckle from a clever play on words, specifically a pun. The setup describes a truly awful scenario – being trapped underground in a watery hole. When the punchline declares, "I know he means well," it twists the common idiom "he means well" (meaning he has good intentions) into a literal reference to the "well" from the setup. It’s a classic homophone pun, where a word or phrase sounds like another but has a different meaning, creating an unexpected and amusing connection.

The humor hinges on taking a familiar expression and giving it an absurdly literal interpretation within the context of the joke's dark setup. The phrase "he means well" is used daily to describe someone whose advice or actions might be misguided but come from a place of genuine care. Here, the joke uses that familiarity to lull you into expecting one meaning, only to surprise you with a direct, physical interpretation of the "well" itself, leading to that satisfying groan-laugh reaction. It’s a quick, sharp linguistic trick that turns a grim image into a lighthearted moment of wordplay.