Captious
Etymology
From Latin captiosus, "fallacious, deceptive, ensnaring," from captio, "a taking, a catching, a fallacy," ultimately from capere, "to seize or take." The original idea was of an argument designed to trap or catch someone out. From "apt to ensnare with tricky points," it broadened to the character of a person forever looking to catch others in small faults.
adjective · /KAP-shus/
Inclined to find fault, raise trivial objections, or catch people out in petty errors.
What it names
The temperament of the nitpicker who greets any statement by hunting for the small flaw to pounce on.
Example
His captious editing flagged every comma while ignoring whether the argument actually held together.
Related idea
Critical can be fair and substantive; captious is critical in a mean, small-minded way — fault-finding for its own sake.