A jarring event took place in NYC on Saturday … when an apparent lookalike contest was held — and very much attended — for the suspect who killed the UnitedHealthcare CEO Brian Thompson in cold blood this week.

Online reaction to the gathering is a mixture of shock and celebration … putting a fine point on how polarizing the murderer has become.

Several people in Washington Square Park came dressed in clothing that resembled what the suspect — who remains at large — wore when he fatally shot Thompson outside his hotel.

One attendee wore a shirt that read “Deny, Defend, Depose” … the same words written on the shell casings of the bullets used to assassinate Thompson.

While it might be considered to be in extraordinarily poor taste and completely heartless … the lookalike contest is hardly surprising, given how many have celebrated the slaying due to their bitter feelings toward insurance companies.

TMZ reported Saturday that internet sleuths believe they have found the jacket worn by the gunman … and now it is morbidly flying off the shelves.

NYPD Chief of Detectives Joseph Kenny told reporters Friday that detectives are looking into the possibility the gunman used a veterinary gun … a larger gun commonly used on ranches and farms — but the gun hasn’t been recovered.