Aside from the monkey-see-monkey-do school of misinformation, where do people like you get the idea that words like nonfat are hyphenated? Certainly not in any dictionary of American English that I ever saw. Mine, for instance, has upwards of a thousand such words from nonabrasive to nonzealous. This matters because innocent, impressionable children will see your blunder and imitate it. Give good example to America's youth, not bad.
I can easily defend my choice to hyphenate this word by saying it is a sign written by the character in the comic. It was his mistake, not mine. But that would be dodging responsibility for my callous and foolhardy behavior that most certainly has poisoned any number of young minds. So please accept my heartfelt apology for this grievous error. As of this day, I will no longer be asking my monkey (seen above driving a truck) about issues of punctuation and I encourage you parents out there to advise your children to do the same.