When you intentionally leave without saying goodbye.
You're at a party, and you want to go home early. You know that if you go say goodbye to your friends, they will try to convince you to stay longer. So instead you slip out without anyone seeing you leave. When your friends realize this, they will say that you did a "Puerto Rican" or "Puerto Rican Fade"
This is a phrase used in South Africa. I'm not sure if its used anywhere else in the world. I cant seem to find the origins.