An assistant school principal slashed a man who was sitting in a car on a Staten Island street, police sources said Sunday.

Vincent Scotto, 43, was charged with assault and criminal possession of a weapon after slashing the other man in Great Kills during a dispute at about noon Saturday, police said.

The Department of Education employee reached in the 59-year-old man’s side window and slashed his left arm with a razor blade in front of 150 Greaves Ave., the sources said.

It wasn’t clear what the men were fighting about.