The post on Twitter appeared innocuous enough for a New York City agency tasked with taking complaints about police officers: a “Star Wars”-themed reminder on May 4 that the Fourth Amendment of the United States Constitution prohibits unreasonable searches and seizures.

“May the Fourth Amendment be with you,” the message read in the classic yellow type of the movie franchise, above a photograph of a diverse group of young men and women who work at the agency. The message included a link to where a complaint against New York Police Department officers could be filed.

That was too much for Edward D. Mullins, the outspoken head of the union representing sergeants with the Police Department.

“You are all a disgrace,” he replied on Twitter hours later, using the official account of his union, the Sergeants Benevolent Association. “You sit on your ass and target the N.Y.P.D. all while growing up on the nipple of what’s easy.”

“One day you will dial 911 when evil is at your door and thank god for the N.Y.P.D.,” he added.

Thousands responded — many angered by Mr. Mullins’s message, others defended him — in a torrent of vitriol and internet-memes that included some less-than-thoughtful observations on race and policing as well as the requisite name calling and scatological humor. Many were taken with Mr. Mullins’s reference to the old notion of living off the government teat.

Others said it was curious the leader of a police union would object to a public service announcement about a constitutional right. “This tweet is — in and of itself — evidence that you didn’t understand your job in even the tiniest amount,” wrote Gautam Mukunda, a Harvard business professor. “America is not a police state. American citizens have rights.”

Not keen on joining the debate, which reached far beyond New York City: the local police oversight agency whose members were attacked. A spokeswoman for the Civilian Complaint Review Board, Colleen A. Roache, declined a request for comment. So too did the Police Department’s top spokesman and City Hall officials.

“City Hall isn’t in the business of responding to every little thing this union official says,” said Eric F. Phillips, the press secretary for Mayor Bill de Blasio.

Mr. Mullins, who last year faced criticism for decrying “blue racism,” was happy to discuss his reasons for posting the Friday night message that set off a Twitter storm. And he demanded an apology from the employees of the board.

“I was in my home office going over the Twitter account and I noticed that one,” he said in a telephone interview on Sunday. “I shortly afterward started to get notification from other police officers who were upset by it.”

He decided to post a response, he said.

“They made a comment about N.Y.P.D. officers: that’s painting a picture and brushing everyone the same,” Mr. Mullins said, unconcerned that his own message had much the same affect on the city employees, accusing them of personal laziness.

He said he stood by his comments despite the backlash. “People can say what they want,” he said. “They don’t know Ed Mullins.”