A waddup gangsta is a term used to describe a certain type of gangsta. This particular type of gangsta is the kind seen with baggy clothes, bopping his head to cRAP music, and who is quite obviously caucasian.
Example #1-Renée says:"Check it out, i got some waddup gangstas living across the street."
Maddy says:"Waddup gangsta!!!!"
Example #2-Maddy says:"Check out that waddup gangsta being arrested by the Po."
Renée says:"Waddup gangsta!!!!"