Throwing a shoe, for me, is not assault. It seems more like he was trying to put the lowest cultural shame on him that he could. I totally got it and died laughing. He didn't get hit and even if he did, he would have at worst just had a knot in the head.
Maybe if he had been used to having shoes flung at him in his youth (particularly toward his backside, as many people I know have experienced) he would have been a better president? Juss sayin'...