I used to be a banker

This one-liner thrives on clever wordplay, a fundamental humor mechanism. The punchline hinges on the double meaning of the word "interest." In the financial world, "interest" refers to the money earned on savings or paid on loans, a concept central to banking. However, "interest" also means enthusiasm, engagement, or curiosity. The comedic twist comes from the unexpected shift from the financial definition to the emotional one, creating a quick, satisfying realization for the listener.

The world of banking, while essential, is often perceived as serious, number-driven, and perhaps a bit dry. Bankers are professionals who deal with money, investments, and, naturally, interest rates. The setup establishes this professional background, making the subsequent pun even more effective because it takes a common term from that specific field and flips its meaning entirely, injecting a dose of unexpected human emotion into a typically stoic profession.

This kind of joke is a prime example of why puns are so enduring in comedy. They're concise, require minimal setup, and deliver a quick burst of amusement by playing with language. The humor isn't about absurdity or irony, but purely about the linguistic gymnastics, making you chuckle at the cleverness of the word choice and the swift semantic pivot.