A "black accent"; When a worker, generally of African American race, at a low-level job has horrible customer service skills and shows his/her misery by mumbling or speaking improperly, and then proceeds to get annoyed when you can't understand what he/she said.
Customer: Hi, I'll have a burrito bowl to go.
Worker: mumbles incoherently*
Customer: Excuse me?
Worker: I SAID WHITE OR BROWN RICE
Customer: relax, it's not my fault you're speaking with a blaccent