We've talked about km before and his penchant for intentional headshots, its plainly evident that some of them are intentionally aimed as such.
Yes face pro is a valid point, and it is a risk you take, but it is not a defence for being a dick.
I always hold that you should shoot centre of mass of what you can see, if all you can see is their head then it's a valid target, but if they give you something else to shoot at go there first, which in some of his videos this is a thing he evidently does not adhere to.