I'm not sure if I've ever had to explain what it is to any of the cis people in my life. Most of them have, at the very least, a working understanding of what the concept is and what it means. I usually instead explain how it relates to my life, and inevitably I tend towards metaphor and simile. I think if I ever end up having to explain the concept itself, I'm probably going to go all lawyer on it, and bludgeon my audience with as many facts and citations as possible. Also, metaphors and similes.
I really, really like using metaphors and similes. Maybe I was a poet in a past life?