One of the only phrases a man can say to comfort himself after a woman does something irrational, ignorant, or insane. It is used to laugh away the confusion a "bitch" inflicts upon a perfectly sane man.
Marcus: "Taylor is driving me crazy man! She doesn't make any sense."
Jordan: "Well, you know how it goes man..."
Marcus: "Yeah, bro..."
Jordan: "Bitches be crazy."