I went on a date with a calendar.

This joke hinges entirely on a clever bit of wordplay, taking advantage of the double meaning of the word "dates." In the setup, the speaker is referring to a romantic encounter, a "date" with a personified calendar. The punchline then pivots to the calendar's actual function, where "dates" are specific days of the month, which are, by their very nature, always predetermined and set in advance. The humor comes from this unexpected, literal interpretation of the calendar's job applied to a social situation.

The real-world context here is, of course, dating and the often-complex world of romantic relationships. While we might joke about people who have "pre-arranged" or overly scheduled lives, a calendar literally has every single day, or "date," already laid out and organized. The absurdity of trying to have a spontaneous romantic connection with something designed for rigid scheduling creates a lighthearted contrast that makes the pun land.

It’s a classic example of how a simple linguistic trick can create a chuckle. The joke doesn't rely on complex scenarios or deep cultural references, just a straightforward understanding of a common word used in two very different, yet equally valid, contexts.