affectionate names for people's pets.
Hey, Fruity. Get off of there, you nutty cat! Cm'on here, furr ball. What do you think that you are doing, being a cat or something? Yea, don't give that look, you know that you were on the table again. You are such a goofy cat. ... You know that we love you - silly cat. You are a member of our family - Yes you, you are the Fruitnut of the world. Cats make the word a better place to live.
A fruitnut is someone who either acts dumb or is dumb. However, they are fully competent of not being dumb!
A fruitnut is sort-of a nicer way of saying dumbass.
That guy is such a fruitnut! He doesn't understand the difference between a sunny day and a hot day.