Etheridge reacted poorly. I think there is no real question there. I do to an extent feel for him. Just because you are a public official does not mean people should be able to try and get an on camera interview any time they want. The kid was being a dick. That does not excuse Etheridge's behavior, but he was not the only one whose behavior was inappropriate.
"He who does not think himself worth saving from poverty and ignorance by his own efforts, will hardly be thought worth the efforts of anybody else." -- Frederick Douglass, Self-Made Men (1872)
Etheridge reacted like an idiot. The kid was being a prick, but the proper response would have been to ignore him or sling some verbal insults his way. I personally don't consider what he did to be serious enough to get the police involved, but the law is the law and he should receive no special treatment for his political status.
And again, this does not excuse his behavior. If he has said "I don't have time", or even "**** off and leave me alone here" I would not have had a problem with it, but to grab the kid, that is simply wrong.