Re: One Piece Mega Convo (Spoilers!)
About the scar, as Razh said it can't have happend before Smoker ate the DF because we saw him around chapter 100 and it was NOT there. Arguing out of the manga we would have to assume Oda made a mistake, but there are clearly other possibilities like strong enemies or someone getting hold of his jitte during a fight and hurting him!
About the other incident, well that was discussed to death here and in the tree of knowledge. While the theory of haki is nice, there is no proof for it whatsoever. Luffy wanted food. propelled himself forward and hit them while they were not aware of the 'danger' in their backs, which is what some assume is the reason why their intangability failed.