What term describes a person who habitually engages in critical or fastidious behavior?

The term that best describes a person who habitually engages in critical or fastidious behavior is "fastidious." This word denotes someone who is very attentive to detail and often hard to please due to their picky nature. Fastidious individuals tend to be meticulous in their work or personal standards, frequently finding fault in small imperfections, which aligns perfectly with the idea of being critical or demanding in a habitual way.

While "exacting" could also relate to someone who has high standards, it typically describes a demand for precision or strictness rather than the overall critical demeanor associated with fastidiousness. "Judgmental" implies a tendency to form opinions about others, often in a negative light, but does not necessarily capture the detail-oriented aspect that fastidious encompasses. "Nice," on the other hand, contrasts sharply with the concept of being critical, as it generally refers to someone who is pleasant or agreeable rather than exacting in their criticism.