I have a t-shirt given to me by my older daughter quite a few years ago. It is a keepsake because across the chest is this notice: "Careful Or You'll End Up In My Novel." And my point to you, if you're a writer, is this: it's too late to warn people. Whether you realize it or not, your characters come out of your imagination gently supplemented from experiences with real people. And that's a problem, too. Mordecai Richler said this on the topic: "If you caricature friends in your first novel they will be upset, but if you don't they will feel betrayed."
I did that in my first novel, Signs of Struggle. And subsequent novels, too. But you'll never get me to confess.
So go ahead, writers, and tap into your experiences and observations involving real people you know. Your writing will be richer for it. Just have a good defense lawyer on speed dial.