Theo Von Grabs Fan by Throat in Nashville Bar, on Video

Comedian Theo Von was in no laughing mood when he grabbed a fan by the throat at a Nashville bar earlier this month -- and we have the disturbing altercation on video.

Check it out ... a man holding some birthday balloons goes up to Theo but doesn't back down after a quick back-and-forth, clearly antagonizing him.

Theo looks like he wants to be left alone, and just seconds into the video you see him wrap his right hand around the man's neck and firmly push him back.

The 'This Past Weekend' podcast host stares the victim -- who is clearly shocked by being manhandled -- down and gives him a piece of his mind before the video cuts off.

And if there's any question about Theo's intentions, one eyewitness tells TMZ he used "crushing force" and was not playing around.

However, a source with direct knowledge tells us the guy with the balloons was with a group of people who had repeatedly harassed the comedian. We're told they continued antagonizing Theo and used threatening language ... saying they were trying to screw with him on camera.

The altercation went down at The Twelve Thirty Club in Nashville on May 2 -- one day before Theo brought his stand-up tour "Return of the Rat" to Bridgestone Arena right across the street.

TMZ spoke with the Metropolitan Nashville Police Department, who confirmed they responded to a misdemeanor assault complaint about the incident on May 4. The investigation determined there will be no action taken concerning the complaint.