A nagger is someone who annoys you and does the act of nagging. In the show South Park there was a very controversial episode where Stan’s dad Randy Marsh is on wheel of fortune and has to solve the puzzle. "People who annoy you" (N*ggers). And Randy answers "niggers". But then realizes the answer was naggers.
"Clean your room! do the dishes, mow the lawn!," said Timmys mom. "no mom stop being such a nagger" said Timmy.