fun size?

You know when Halloween comes around you are going to buy those fun size candies. All your favorite candy bars come in bite sized pieces. Since when did we institute "fun"as a unit of measure? Imagine using that in everyday job type speech. I could tell the contractors, "yeah, the reveal is about a fun size" or "the joists are spaced 26 fun sizes." Those are terrible examples by the way. But did you ever notice that whenever someone buys a bag of fun size candies there's Krackel, Mr. Goodbar and regular Hershey's milk chocolate, and everybody always goes for the Krackel or Mr. Goodbar first? But in real life, no one ever craves a Krackel or a Mr. Goodbar. Come to think of it, I have only ever seen them in that fun size bag.