'Ellen Dance Dare' Contestant SHOVED by Cop ... NYPD Investigates

12/30/2014 1:25 PM PST

'Ellen Dance Dare' -- Contestant SHOVED by Cop ... NYPD Investigates (VIDEO)

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The NYPD is looking into why an officer got physical with a guy who was filming a viral video for "The Ellen DeGeneres Show."

The dancer is Alexander BOK, and he bills himself as "your favorite prankster" ... that is unless you're one of the cops he attempted to bust a move on in the middle of a NYC street.

On Christmas Eve, Alexander tried to film an Ellen Dance Dare video -- entrants are supposed to dance behind people who don't know they're doing it. Alexander decided to try it on some unwitting officers.   

Watch the video ... the officers start out questioning what the hell Alexander's doing -- and it sounds like they hurl a few insults at him too. Eventually, it looks like the cops dismiss him ... and, as he's walking away, one throws him to the ground. 

TMZ has learned NYPD has opened an investigation into the incident. What's unclear is why Alexander chose to pull this stunt four days after two NYPD officers were assassinated. Not a bright move.

Alexander tells TMZ he submitted his video to the show, but has yet to hear back.