Rudy Giuliani erupted on a heckler during a parade to celebrate Israel on Sunday, calling the man a “jackass” and a “brainwashed a-hole” while defending his record as the city’s mayor.

Giuliani could be seen on video shouting at the unidentified man at 5th Avenue and 62nd Street after the heckler got under his skin during the Israel Day Parade.

“Crime was down 55% under me, it’s up 40% under him,” he shouted while leaning over the police barricades, in apparent references to Mayor Eric Adams and recently released NYPD data.

It’s unclear what the man said to Giuliani — the ex-personal lawyer for former President Donald Trump — that prompted him to yell back in fury.

The recent “Masked Singer” contestant and critic of Mayor Eric Adams then shouted: “I reduced crime, you jackass!”

A 35-second video posted on Twitter by The Forward reporter Jacob Kornbluh captured the exchange.

During his tenure at City Hall, Giuliani and then-Police Commissioner Bill Bratton implemented a new data system for the NYPD. The system is credited with helping crime rates plummet in the mid-to-late 1990s.

After taking a few steps along the parade route as his girlfriend — Maria Ryan, wearing a red “Giuliani” hat — appeared to try to coax the former mayor to move along, Giuliani yelled, “You are a brainwashed a-hole!”

The former mayor then gave his miniature Israeli flag a wave and concluded his eruption with, “and you are probably as demented as [President Joe] Biden!” before continuing to walk in the parade route while smiling and waving the flag above his head.

Giuliani’s clash with a critic came during the return of the Israel Day Parade after a two-year COVID-19 pandemic-induced hiatus.

On Sunday, thousands of Israel supporters marched up Fifth Avenue from 57th Street to 74th Street while chanting and hoisting Israeli flags in the Celebrate Israel Parade. The event was organized by the Jewish Community Relations Council of New York and began in 1964.

Adams was among the several politicians who participated in the march. 

“It’s lovely being here, it’s a great parade, I look forward to it every year,” the mayor said in a video posted on the parade’s Twitter account.

Gov. Kathy Hochul, state Attorney General Letitia James, as well as U.S. Reps. Carolyn Maloney (D- Upper East Side) and Jerry Nadler (D- Upper West Side) also attended the event, a photo shows.