The word for a pedantic person who raises questions and objections, and causes difficulties or problems over things of little importance is piantagrane in Italian. Some possible translations in English include troublemaker, fault-finder and nitpicker.
Piantagrane is the combination of the verb piantare (to plant) and the noun grana, which in addition to meaning ‘grain‘ is also a familiar way of saying ‘trouble‘ or ‘hassle‘.

Piantagrane is an invariable noun whose form does not change in the feminine or plural.
il / la piantagrane
the troublemaker
un / una piantagrane
a troublemaker
i / le piantagrane
the troublemakers
dei / delle piantagrane
(some) troublemakers
A closely related idiomatic expression is piantare una grana (lit. to plant a grain), which means to stir up trouble.
Dai, finiscila di fare il piantagrane! Non hai niente di meglio da fare?
Come on, stop being a troublemaker! Don’t you have anything better to do?

Some synonyms for piantagrane include:
- pedante = pedantic
- rompiscatole = pain in the neck (as well as the more vulgar rompiballe and rompicoglioni)
- persona cavillosa = pedantic / small-minded person
- seccatore = pest