My dad told me he was going to make a belt out of watches.

This joke is a classic example of wordplay, specifically a pun, which is a humorous play on words that sound alike but have different meanings. The setup describes a rather unusual project: making a belt from watches. This immediately sets up the listener for a connection between belts and the body part they encircle – the waist.

The punchline brilliantly exploits the phonetic similarity between "waist" (the part of the body where a belt is worn) and "waste" (to use or expend carelessly). Since the belt is being made from watches, which are instruments for telling time, the phrase "waste of time" perfectly fits the context, creating a clever double meaning. It's a playful jab at the dad's potentially impractical craft project, suggesting it's not only a physical "waist" of watches but also a "waste" of effort. This kind of humor relies on the audience making that quick linguistic connection.