Can you believe the comments of our UN ambassador Susan Rice about the Libyan killings ?

[say yes to tacos]

The "who brings RPG's to a protest?" angle is easily answered: opportunists.
Protests are known for having lunatic fringes that are emboldened by the anonymity of large gatherings.
As far as the anti-Islam film explanation - it is entirely likely that it was used to inspire open discontent
in the hope of escalating violence towards America. In this regard, the UN ambassador was correct, the protests WERE in response to the film; perhaps it was part of a bigger plan which we are unaware of yet - but since a gov officials job isn't to publicly speculate, Rice is factually correct.