A Manhattan numbskull strolled into Queens court Thursday with a fake grenade Thursday, drawing an immediate response from the bomb squad, law enforcement sources said.

David Herbsman, a 22-year-old from Inwood, set off metal detectors with his novelty item at about 3 p.m. at Queens Criminal Court in Kew Gardens, police said.

He was arrested on charges of placing a false bomb and creating a criminal nuisance.