What does 'to be a story' means?

Could you explain to me, please, what the expression "You are a story" means, used in the following dialogue:

A: “You mustn’t pay any attention to old Addie,” she now said to the little girl.
B: “She’s ailing today.”
A: “Will you shut your mouth?” said the woman in bed. “I am not.”
B: “You’re a story.”