Definitions

1. adjective

given to or characterized by fastidious or exacting standards, especially in a trivial or annoying way

“She’s a very fickler customer, always complaining about the smallest details.”

2. noun

a person who is given to or characterized by fastidious or exacting standards, especially in a trivial or annoying way

“He’s such a fickler that he can’t even decide what to eat for dinner.”