1. The most derogatory definition for wunani is the lowest form of cowardice attainable by the human race. Simply said, a wussy-pussy.
2. A more common usage would be someone who is cowardly for extremely stupid reasons like evading the police for having a suspended license, or shaving off all your hair because the court has requested you be drug tested.
-Hey, bro... where did the last beer go?
+Uhhh...I don't know.
-What's that in your hand? You're such a wunani. You should've called me on my way here. i would've pick up some beer and refrigerator crack before i came over.
+sorry bro. I know.