Formal:
* Cavil: To make petty or unnecessary objections.
* Nitpick: To find fault with minor details.
* Fussy: To be excessively concerned with small details.
* Hypercritical: To be excessively critical, often in a petty way.
Informal:
* Pick at: To find fault with something in a persistent or annoying way.
* Find fault: To be critical of something, often in a petty way.
* Quibble: To argue about trivial matters.
* Carp: To complain constantly, especially about unimportant things.
* Bicker: To argue about something unimportant in a petty or annoying way.
* Nag: To repeatedly complain about something, often to someone specific.
Other options:
* Hair-split: To argue about minute differences.
* Pedantic: To be overly concerned with minor details, especially in a way that is annoying or pedantic.
* Belittle: To make someone or something seem unimportant.
The best word to use will depend on the specific context and the desired tone.