I knew a guy who collected candy canes. They were all in mint condition.
Why this joke works
A Collector with Excellent Taste
Collectors use mint condition to describe an object that looks as good as new. Candy canes make mint available as a flavor instead, so an apparently serious report on a collection becomes a taste description. Collected is doing important setup work: it encourages us to imagine careful storage and prized specimens. Without that collector framing, the final phrase would still mention candy, but it would lose the little change from assessing an object's condition to thinking about its ingredients.
A closer look
A Closer Look
Treat the collector as someone with a perfectly respectable hobby. The straight-faced introduction makes the last sentence sound like an appraisal until the flavor connection catches up. This fits naturally alongside holiday sweets or a stocking-stuffer note. It assumes peppermint-style candy canes; fruit-flavored varieties would weaken the reason that every item supposedly shares the same condition.
Fact behind the joke
Fact Behind the Joke
The U.S. Mint distinguishes proof coins from uncirculated coins by how they are produced, not simply by their age. Proof refers to a specialized minting process. Collectors therefore have a richer vocabulary than merely calling everything mint. The joke borrows that world of carefully described objects and applies it to a candy collection.