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"
Useless information (i.e. 0-60 times of cars, heights of the tallest buildings) that you can throw out in a pub/bar/whatever to impress your friends.
It also may include feats of strength that you've done, dares that you didn't chicken out of and exploits with the ladies that you aren't embarrassed to share.
That dude was spitting some serious pub ammo after a pint of Guinness.