Cats hack up plenty of things on their own, and cat owners sure don't need an increase in volume because of something simple like an avocado. Guacamole and several other human foods can make cats sick.
I had a dog once that ate half a bag of coffee grounds and miraculously survived. Don't let your dog get into that! Caffeine can cause serious problems for pets, along with chocolate, plants, meds, and a few surprise items around the house.