(informal) small and of little importance "a dispute over niggling details" - fiddling, footling, lilliputian, little, piddling, piffling, petty, picayune [N. Amer], trivial
Verb: nigglenigul
Worry unnecessarily or excessively - fuss, fret
Argue over petty things - quibble, pettifog, bicker, squabble, brabble