When someone else does a favor for you and you wanted them to know that they just got owned. Can be also used when someone does something for you and you simply must feel superior to them. Popularized by Nicole Richie on a commericial when she simply replyed "thanks bitch" when Jessica Alba tore up all those paparazzi.
"Can you please return this to her really quick...thanks bitch."
Joe - " You forgot your cell in my car fool"
Blow - "Thanks bitch"