Not completely sure what's going on here, but it looks like NY-1 attempted to interview Rep. Michael Grimm about some campaign finance allegations. Grimm refuse to talk on that subject and walked away. A few seconds later, Grimm, apparently thinking the camera was no longer rolling, approaches the reporter and gets in his face in a rather aggressive manner. The audio isn't understandable, but the body language does appear to be threatening, and the reporter sounds alarmed.
Politicians, gotta love how they behave when they think cameras aren't on them.
UPDATE: Consensus on Twitter seems to be that Grimm told the reporter, "You're not a man. I could break you in half." The audio on this version of the video is clearer: