expletive; specifically when one has been offended by an institution or larger group of people. Can also be used as an exclamation, similiarly to "well I'll be darned". Also occasionally used as a plural noun.
Avid movie-goer: "can i have two tickets for 'movie' please?
Ticket seller: "I'm sorry sir, we're sold out for the next two days"
Avid movie goer: (to no one in particular) "buncha bitches!"
Tourist upon seeing the grand canyon for the first time:
Kid A: "How come Mike's friends are so stuck up and mean?"
Kid B: "Oh, they're a buncha bitches."