Avocado

This week a question came in from a student at my Santa Monica College class:

"I am wondering what is the best time (or how do I know when) to pick an avocado [off a tree]. Thanks and I really learned a whole bunch in your class! Best, John"

Now I confess, I told John to send his question in to Ask Gardenerd because I didn't know the answer. We joke around here at Gardenerd that if I can't ...