What word describes a peevish or ill-behaved attitude?

The word that describes a peevish or ill-behaved attitude is "petulant." This term specifically refers to a disposition characterized by sudden, impatient irritation or annoyance, often over trivial matters. When someone is petulant, they may display a tendency to sulk or behave in a moody and irritable manner, which aligns with the idea of being ill-tempered or difficult. This term often captures the essence of childish or unreasonable behavior, making it particularly apt for describing such an attitude.

In contrast, the other choices do not convey the same meaning. "Pithy" refers to language that is concise and forcefully expressive, which does not connect to the idea of behavior. "Peculiar" suggests something strange or unusual, without any implication of irritability or bad behavior. "Plumb," while it can refer to the act of measuring depth, does not relate to attitude at all. Thus, "petulant" is the only option that accurately encapsulates a peevish or ill-behaved attitude.