A Queens cop is suing the city — claiming a hot-headed fellow officer pulled a gun on him.

When South Task Force Officer Joseph Giordano, a 14-year NYPD vet, returned from patrol to the unit’s Rosedale headquarters last April, Thomas Hopper, assigned to the switchboard, asked if he was his meal-break replacement, sources said.

When Giordano said no, Hopper allegedly instigated a fight, then pulled his gun. He was suspended.

Giordano is seeking unspecified damages.

The city did not immediately respond to a request for comment.