I’ve tried a lot of the “newer” languages and, somehow, I’m always happiest when I go back to C++ or even C. However, there is one thing that gets a little on my nerves when… ...

Statements are executable and can have breakpoints set on them. Everything else can't.* Really the non-executable stuff in a header is no different than the non-executable stuff in a source file.

Basically once you've put a using namespace std; in your header, and someone has included your header, there's no way to undo the using. This can reduce your options when a name conflict occurs.