Which word best describes someone who is difficult to please?

The term "martinet" refers to a strict disciplinarian, especially in the context of someone who enforces rules and regulations rigorously. A person described as a martinet is typically inflexible and expects a high standard of behavior and performance from others, which can make them seem difficult to please. This aligns perfectly with the idea of someone who is hard to satisfy, as they may not easily accept anything less than their own stringent expectations.

In contrast, the other options do not encapsulate the notion of being hard to please in a personal or subjective sense. "Obviate" means to prevent or make unnecessary, which does not relate to someone's temperament regarding satisfaction. "Reprehensible" describes something deserving condemnation or criticism and does not address a person's demeanor. "Somber" indicates a serious or gloomy disposition, which is unrelated to the ability or willingness to be pleased. Thus, "martinet" is the most fitting choice for someone who is difficult to please.