It's not just that the congressman (I won't capitalize it in this case; he doesn't deserve it) takes the kid's camera phone away from him and grabs him around the neck (though those things are bad enough); it's not even that, as many people have already noted, the guy appears to be more than a little tipsy. The thing that stands out to me is the smarmy sense of entitlement that seems to ooze from every pore in the man's body, like he's some sort of royalty who can't possibly be bothered to field a question from a mere commoner.
There were so many better ways to handle this; simply saying "no comment" and walk away or inviting the questioner to call his office would have been the best way. But no, this guy did something that would appear to rise to the level of assault and battery, and I hope he gets brought up on charges for it (though I'm not holding my breath).
These guys need to remember something: You. Work. For. Us. A whole bunch of people need to get sent packing this November, and Etheridge is definitely among them. It's time to take our country back.