The phrase "my hovercraft is full of eels" is a classic example of anti-humorous or anti-joke. It's meant to be a nonsensical statement that, instead of being funny, just confuses the listener or makes them feel perplexed.

In the original context, this phrase was used in a 1970s British television comedy sketch called "The Two Ronnies." One of the characters says this line, and the other replies with another unrelated fact. The purpose is to demonstrate how two people might have an absurd conversation without any real connection between their statements.

Since then, it has become a well-known phrase in various cultures for its absurdity or lack of humor. People often use it when they want to say something that seems unrelated or nonsensical, not intending to be funny but rather to change the subject or to show disagreement or confusion.

So, while the statement itself doesn't make logical sense (hovercrafts shouldn't be full of living creatures like eels), its popularity comes from how effectively it can derail a conversation or express absurdity.