In a novel called "Pattern Recognition" by William Gibson is the paragraph:
Seated, not bothering with the menu, Cayce orders coffee, eggs, and sausage, all in her best bad French.
The girl looks at her in amazed revulsion, as though Cayce were a cat bringing up a particularly repellant hairball. "All right," says Cayce, under her breath, to the girl's receding back, "be French."
What does "be French" mean here?