Madame Pomfrey is the always harried and often foul-tempered school nurse at Hogwarts. We can't really blame her for her bad mood – the woman has a rather thankless job.
Just think of how many wacky injuries and illnesses she has to deal with on a daily basis. In this book alone she was up against a melodramatic Draco Malfoy, people dealing with varying degrees of Dementor exposure (including Harry, who passes out around them), a kid who fell off his broom at a Quidditch match (Harry again), and a group of kids who managed to get beat up by an angry tree (The Whomping Willow). To top it all off, her infirmary was frequently invaded by unruly visitors (Exhibit A: Professor Snape, bellowing like a nut after Black escapes). Madame Pomfrey definitely deserves a raise.