"Fun sized" is small.
This is interesting in several ways.
The original "fun sized" is a lie from candy manufacturers. They didn't want to be honest and say "smaller size," so they called it "fun sized."
Nobody ever looked at a piece of candy and said "Gee, this candy is more fun than the normal size because it's smaller."
Now, "fun sized" is sort of a sarcastic way to say "small." When you apply it to providers, it means small. When a fat provider uses the original lying term "fun sized" to mean large instead of "small," it's sort of a lie on a lie. Do two lies make a truth?
Of course, BBW is a lie, too. It doesn't mean "beautiful," it means "overweight." However, the term has been misused so much that pretty much everyone understand what BBW means. No one would be confused if you said "she's a really ugly BBW," or "a beautiful BBW."